# Cosmic Times Teachers' Guide

# Table of Contents

Cosmic Times Teachers' Guide [1](#cosmic-times-teachers-guide)

Table of Contents [2](#__RefHeading___Toc86911891)

1919 Cosmic Times [4](#cosmic-times)

Summary of the 1919 Articles [5](#summary-of-the-1919-articles)

Sun's Gravity Bends Starlight [5](#suns-gravity-bends-starlight)

Sidebar: Why a Total Eclipse? [5](#sidebar-why-a-total-eclipse)

Mount Wilson Astronomer Estimates Milky Way Ten Times Bigger Than
Thought
[5](#mount-wilson-astronomer-estimates-milky-way-ten-times-bigger-than-thought)

Expanding or Contracting? [5](#expanding-or-contracting)

In Their Own Words [5](#in-their-own-words)

Notes on the 1919 Articles [6](#notes-on-the-1919-articles)

Sun\'s Gravity Bends Starlight [6](#suns-gravity-bends-starlight-1)

Sidebar: Why a Total Eclipse? [7](#sidebar-why-a-total-eclipse-1)

Mount Wilson Astronomer Estimates Milky Way Ten Times Bigger Than
Thought
[8](#mount-wilson-astronomer-estimates-milky-way-ten-times-bigger-than-thought-1)

Expanding or Contracting? [9](#expanding-or-contracting-1)

In Their Own Words [9](#in-their-own-words-1)

1929 Cosmic Times [11](#cosmic-times-1)

Andromeda Nebula Lies Outside Milky Way Galaxy
[12](#andromeda-nebula-lies-outside-milky-way-galaxy)

Universe is Expanding [12](#universe-is-expanding)

"Great Debate" Resolved [12](#great-debate-resolved)

The Minds atop Mount Wilson [12](#the-minds-atop-mount-wilson)

Classifying Nebulae [12](#classifying-nebulae)

In Their Own Words [12](#in-their-own-words-2)

Notes on the 1929 Articles [13](#notes-on-the-1929-articles)

Andromeda Nebula Lies Outside Milky Way Galaxy
[13](#andromeda-nebula-lies-outside-milky-way-galaxy-1)

Universe is Expanding [15](#universe-is-expanding-1)

Sidebar: \"Great Debate\" Resolved [19](#sidebar-great-debate-resolved)

The Minds atop Mount Wilson [20](#the-minds-atop-mount-wilson-1)

Sidebar: Classifying Nebulae [20](#sidebar-classifying-nebulae)

1955 Cosmic Times [26](#cosmic-times-2)

'Yardsticks' in Neighbor Galaxy Double Universe's Size
[27](#yardsticks-in-neighbor-galaxy-double-universes-size)

Origin of Everything [27](#origin-of-everything)

Hoyle Scoffs at "Big Bang" Universe Theory
[27](#hoyle-scoffs-at-big-bang-universe-theory)

Death of a Genius: Albert Einstein 1879 - 1955
[27](#death-of-a-genius-albert-einstein-1879---1955)

It's a Star! It's a Nova! It's Super-nova
[27](#its-a-star-its-a-nova-its-super-nova)

Radio 'Ear' on the Universe Being Built
[27](#radio-ear-on-the-universe-being-built)

Notes on the 1955 Articles [28](#notes-on-the-1955-articles)

\"Yardsticks\" in Neighbor Galaxy Double Universe\'s Size
[28](#yardsticks-in-neighbor-galaxy-double-universes-size-1)

Origin of Everything: Hot Bang or Ageless Universe?
[29](#origin-of-everything-hot-bang-or-ageless-universe)

Sidebar: Hoyle Scoffs at \"Big Bang\" Universe Theory
[31](#sidebar-hoyle-scoffs-at-big-bang-universe-theory)

Death of a Genius: Albert Einstein 1879-1955
[31](#death-of-a-genius-albert-einstein-1879-1955)

It\'s a Star! It\'s a Nova! It\'s Super-Nova!
[32](#its-a-star-its-a-nova-its-super-nova-1)

Radio \'Ear\' on the Universe Being Built
[33](#radio-ear-on-the-universe-being-built-1)

1965 Cosmic Times [35](#cosmic-times-3)

Murmur of a Bang [36](#murmur-of-a-bang)

Big hiss missed by others [36](#big-hiss-missed-by-others)

Supernovae Leave Behind Cosmic X-ray Generators
[36](#supernovae-leave-behind-cosmic-x-ray-generators)

Quasars: Express Trains to the Netherworld
[36](#quasars-express-trains-to-the-netherworld)

Galaxies Still Misbehaving [36](#galaxies-still-misbehaving)

Notes on the 1965 Articles [37](#notes-on-the-1965-articles)

Murmur of a Bang [37](#murmur-of-a-bang-1)

Big hiss missed by others [39](#big-hiss-missed-by-others-1)

Supernovae Leave Behind Cosmic X-ray Generators
[40](#supernovae-leave-behind-cosmic-x-ray-generators-1)

Quasars: Express Trains to the Netherworld
[43](#quasars-express-trains-to-the-netherworld-1)

Galaxies Still Misbehaving [44](#galaxies-still-misbehaving-1)

1993 Cosmic Times [47](#cosmic-times-4)

Baby Universe's 1^st^ Picture [48](#section-7)

Pancake or Oatmeal Universe -- What's for Breakfast?
[48](#pancake-or-oatmeal-universe-whats-for-breakfast)

Inflation in the Universe [48](#inflation-in-the-universe)

Dark Matter Hunt Heats Up [48](#dark-matter-hunt-heats-up)

Fool-Proofing Galactic 'Candles' [48](#fool-proofing-galactic-candles)

Pulsar Gravitational Waves Win Nobel Prize
[48](#pulsar-gravitational-waves-win-nobel-prize)

Notes on 1993 Articles [50](#notes-on-1993-articles)

Baby Universe\'s 1^st^ Picture [50](#section-8)

Sidebar: Pancake or Oatmeal Universe -- What\'s for Breakfast?
[53](#sidebar-pancake-or-oatmeal-universe-whats-for-breakfast)

Inflation in the Universe [53](#inflation-in-the-universe-1)

Dark Matter Hunt Heats Up [59](#dark-matter-hunt-heats-up-1)

Pulsar Gravitational Waves Win Nobel Prize
[60](#pulsar-gravitational-waves-win-nobel-prize-1)

Fool-Proofing Galactic \'Candles\'
[63](#fool-proofing-galactic-candles-1)

2006 Cosmic Times [66](#cosmic-times-5)

Notes on the 2006 Articles [68](#notes-on-the-2006-articles)

Faster Walk on the Dark Side [68](#faster-walk-on-the-dark-side-1)

Seeds of Modern Universe [73](#seeds-of-modern-universe-1)

Biggest Mystery: What is Dark Energy?
[76](#biggest-mystery-what-is-dark-energy-1)

Sidebar: Sorting Out the Dark Stuff
[77](#sidebar-sorting-out-the-dark-stuff)

\'First Light\' Wins Nobel [78](#first-light-wins-nobel-1)

Journey to Cosmos\' Dark Heart [78](#journey-to-cosmos-dark-heart-1)

# 1919 Cosmic Times

In this first edition of *Cosmic Times*, several concepts are introduced
which will be revisited and built upon in future editions. The first
concept is the idea of Einstein's General Relativity and its first
confirmation. In addition, the idea of the size of the Universe is
introduced. In 1919, the Universe was viewed to contain only the stars
in the Milky Way. Other galaxies had not yet been resolved into their
constituent stars, so it was not apparent that some of the fuzzy nebula
were, indeed, outside our own galaxy. The Universe was a much smaller
place than it is today, but change was just on the horizon.

The language in the 1919 *Cosmic Times* mimics the style of writing that
would have appeared in a real 1919 newspaper. The poster also mimics the
layout of newspapers of the time. We have, however, taken some creative
license to make it more readable in a classroom setting. Real newspapers
of the time would have had 5-7 narrow columns. The size of the text in
each column would have gotten smaller and smaller as you read down the
column, so the more details you wanted, the harder you would have had to
work to read it.

![](media/image1.jpeg){width="3.5in" height="4.813194444444444in"}

## Summary of the 1919 Articles

### 

### Sun's Gravity Bends Starlight

This article discusses the first confirmation of Einstein's Theory of
General Relativity. He had introduced the theory several years earlier
(1915); however, since General Relativity reduces to Newtonian Gravity
except in cases of extreme speeds (i.e. close to the speed of light) or
in strong gravity, the tests of General Relativity were somewhat
limited.

### Sidebar: Why a Total Eclipse?

In day-to-day life, Newtonian gravity is enough to predict how objects
will behave. In order to see the effects of General Relativity,
extraordinary conditions are needed -- either high speeds, close to the
speed of light, or strong gravity. In the early 1900s, the most
accessible test for General Relativity was to watch the behavior of
starlight as it passes very near the Sun.

### Mount Wilson Astronomer Estimates Milky Way Ten Times Bigger Than Thought

In 1919, astronomers did not realize that there were galaxies in the
Universe besides our own Milky Way. That discovery did not happen until
1924. At the time, they thought that stars and nebulae populated the
Universe uniformly. Astronomers had observed nebulae, some of which
appeared spiral, but they could not resolve these nebulae into stars.
There was a debate going on at the time of this issue of the *Cosmic
Times*, as to whether these nebulae were indeed just gas and dust or if
they were comprised of stars. The telescopes of the time were not
sensitive enough to settle the question.

### Expanding or Contracting?

When applied to the real Universe, the equations of General Relativity
predict that the Universe cannot be static -- it must be either
expanding or contracting. While an expanding Universe is an accepted
concept today, it was a radical idea in 1919. Certainly they knew that
the heavens were not unchanging, but it was largely believed that the
Universe, as a whole, was static.

### In Their Own Words

This column includes excerpts from various papers that introduce
concepts that will be built upon in future issues of the *Cosmic Times*.
The quotes may be a little difficult to understand, as they are taken
directly from published papers by the listed authors.

## Notes on the 1919 Articles

### 

### Sun\'s Gravity Bends Starlight

*The primary message of this article is that all theories, even
Einstein\'s, have to undergo testing before they become widely accepted.
This test of General Relativity established not only his theory of
gravity, but also Einstein\'s fame.*

This article discusses the first confirmation of Einstein\'s Theory of
General Relativity. He had introduced the theory several years earlier
(1915); however, since General Relativity reduces to Newtonian Gravity
except in cases of extreme speeds (i.e. close to the speed of light) or
in strong gravity, the tests of General Relativity were somewhat
limited.

The best test accessible to the scientists at the time was to look at
starlight passing by a massive object. The closest object with
sufficient mass was, of course, the Sun. However, in order to view
starlight passing close to the Sun, observations had to take place
during a total solar eclipse -- otherwise, the light of the Sun drowns
out the starlight.

Both Newtonian and Einsteinian gravity predict that the Sun will bend
the starlight, but the extent of that bending is different. The test
proposed by Eddington would observe how much the gravity of the Sun
would cause the starlight to bend.

One possible point of confusion for students is why does Newtonian
gravity predict the bending of starlight at all. Light is composed of
\"photons\", and photons are massless. Therefore, since Newtonian
gravity depends on the masses of the bodies involved, it is generally
assumed that Newtonian gravity would predict that the Sun would not
affect light at all.

To help understand this question, here is a brief history of how
scientists viewed the possibility of the bending of light:

-   Newton suggests the bending of light in his 1704 treatise,
    *Opticks*.

-   Henry Cavendish calculates the bending of light due to Newtonian
    gravity in 1784, but does not publish the result. The only evidence
    of his calculation only surfaced in the 1900s.

-   Johann von Soldner calculates the bending of light as it passes by a
    massive object in 1801, taking 25 pages to do it! The calculation
    uses Newton\'s theory of light as a stream of corpuscles (which have
    mass). However, the mass of the corpuscle (photon) drops out of the
    calculation, and the angle only depends on the mass of the object
    and the closest approach to that object.

-   The angle of deflection turns out to be

$a\text{\textasciitilde}\frac{2m}{r}$

where

-   $m = \text{GM}c^{2}$ (G is the gravitational constant, c is the
    speed of light)

-   M is the mass of the sun

-   r is the closest approach distance of the photon to the sun.

```{=html}
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```
-   This solution is an approximation, because it\'s the first term in a
    series. All of the other terms in the series are much smaller. Von
    Soldner\'s calculation is very close to Cavendish\'s, and to a
    first-order approximation, they are the same.

-   In early 1800s, Thomas Young\'s double-slit experiment showed that
    light must behave as a wave, rather than a particle. At this point,
    it was realized that light must be massless. Clearly, a massless
    particle, in Newtonian gravity, would experience no deflection due
    to gravity.

-   Albert Einstein, in 1911, published a paper called \"On the
    Influence of Gravitation on the Propagation of Light\" (published in
    German), which calculated the effect of gravity on light using the
    equivalence principle, and with did not depend on light having mass.
    His answer in this paper was identical to von Soldner\'s
    approximation. However, this calculation did not include all of the
    equations of General Relativity.

-   In 1915, Einstein finished his theory of general relativity, and
    found that the prediction for the deflection of starlight due to the
    Sun would be twice the prediction he published in 1911.

-   In 1919, Arthur Eddington led one expedition to observe the total
    solar eclipse, and found that the light was bent by the amount
    predicted by General Relativity.

Based on this timeline, prior to the 1919 eclipse, astronomers could
have expected one of three results: no deflection at all, assuming a
massless photon and Newtonian gravity; some deflection, assuming
massless photon that was still accelerated in a Newtonian gravity well;
or full deflection, assuming a massless photon in General Relativity.

It\'s interesting to note that there is some question as to whether or
not the equipment and results of the 1919 eclipse expeditions really had
the sensitivity to detect the starlight deflections that Eddington
claimed. It may be that the researchers injected some of their
expectations into the reported results. However, many subsequent (and
more robust) observations have been performed, all of which confirm the
reported deflection of starlight as that predicted by General
Relativity.

Scientists continue, even today, to put General Relativity to the test,
and all of those tests have added further evidence in favor of General
Relativity.

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Sidebar: Why a Total Eclipse?

*The primary message of this article is that nature offers us
opportunities to test our theories, and scientists take advantage of
those opportunities. The circumstances of the solar eclipse were right
for scientists to test Einstein\'s theory of General Relativity.*

In day-to-day life, Newtonian gravity is enough to predict how objects
will behave. In order to see the effects of General Relativity,
extraordinary conditions are needed -- either high speeds, close to the
speed of light, or strong gravity. In the early 1900s, the most
accessible test for General Relativity was to watch the behavior of
starlight as it passes very near the Sun.

According to General Relativity, light passing near any object with mass
will be deflected, but only the Sun has enough mass for that deflection
to be detectable from Earth, using the technology available in 1919.
However, in order to observe starlight bending near the Sun, astronomers
had to wait for a total solar eclipse. The best way to visualize why is
to consider what the daytime sky looks like. Clearly there are stars
still shining over the entire sky, but none are visible during the
daytime. This is because the light from the Sun is scattered by our
atmosphere, giving us our familiar blue skies. For the same reason,
astronomers cannot observe starlight near the Sun on just any day -- the
Sun is too bright, and the blue sky obscures any attempted observations.

Therefore, to observe stars near the Sun, astronomers needed to wait for
a total solar eclipse. Only during a total solar eclipse is the light of
the Sun blocked out, making stars visible in the daytime.

However, observations during the eclipse alone, would not tell
astronomers if the starlight had been bent. They also needed images of
those same exact stars without the Sun in the way. Then, by comparing
the two images -- one taken without the Sun between the stars and the
Earth, and one taken during the solar eclipse -- they could determine if
the Sun had any effect on the starlight. In addition, if the starlight
had been bent by the Sun, they could determine by how much.

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Mount Wilson Astronomer Estimates Milky Way Ten Times Bigger Than Thought

*The primary message of this article is that at the beginning of the
1900s, astronomers believed that the Milky Way galaxy comprised the
entire Universe. A secondary message is that astronomers must use
indirect methods to determine distances in the Universe.*

In 1919, astronomers did not realize that there were galaxies in the
Universe besides our own Milky Way. That discovery did not happen until
1924. At the time, they thought that stars and nebulae populated the
Universe uniformly. Astronomers had observed nebulae, some of which
appeared spiral, but they could not resolve these nebulae into stars.
There was a debate going on at the time of this issue of the Cosmic
Times, as to whether these nebulae were indeed just gas and dust or if
they were comprised of stars. The telescopes of the time were not
sensitive enough to settle the question.

We now know that some of the nebulae were, indeed, separate galaxies and
there are great distances between the Milky Way and these distant
\"nebula\". However, some of the nebulae are bound clouds of gas and
dust residing in our Milky Way. This question, and its resolution, will
be discussed further in the 1929 issue of the Cosmic Times.

This article also contains the first mention in the Cosmic Times of
Henrietta Leavitt and Cepheid Stars. These stars become more important
in the 1929 and 1955 issues of the Cosmic Times. The 1929 issue
discusses Leavitt\'s observations and their importance in more detail.
Cepheid stars are variable stars that are seen to brighten and dim with
a regular period. Leavitt saw that the period of the variation was
related to the average brightness of these stars. The stars with the
shortest period were dimmer and the longest period stars were brighter.
Leavitt was observing stars in the Small Magellanic Cloud, so they could
all be considered to be at the same distance. This meant that they could
be used as distance indicators, if only a few Cepheids could be found
with a known distance. Shapely was attempting to calibrate this Cepheid
period-luminosity distance scale.

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Expanding or Contracting?

*The primary message of this article is that as he originally developed
it, Einstein\'s theory of General Relativity requires that the Universe
be either expanding or contracting. Because at the time there was no
evidence for such a Universe, Einstein added a correction factor to keep
the Universe static.*

When applied to the real Universe, the equations of General Relativity
predict that the Universe cannot be static -- it must be either
expanding or contracting. While an expanding Universe is an accepted
concept today, it was a radical idea in 1919. Certainly they knew that
the heavens were not unchanging, but it was largely believed that the
Universe, as a whole, was static.

The cosmological constant that Einstein added to the questions of
General Relativity did not affect the results of the 1919 eclipse.
However, Hubble later discovers that the Universe is, indeed, expanding
(as will be discussed in the 1929 issue of the Cosmic Times). George
Gamow, in is autobiography, *My World Line*, says, \"Much later, when I
was discussing cosmological problems with Einstein, he remarked that the
introduction of the cosmological term was the biggest blunder of his
life.\"

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### In Their Own Words

*The primary message of this column is that it is sometimes enlightening
to read a description of the discovery by the scientist who made it.*

This column includes excerpts from various papers that introduce
concepts that will build upon in future issues of the Cosmic Times. The
quotes may be a little difficult to understand, as they are taken
directly from published papers by the listed authors. Here is a little
more on these excerpts and why we have chosen to include them:

-   \"Periods of 25 Variable Stars in the Small Magellanic Cloud\" --
    Miss Henrietta Leavitt

> Cepheid variables are mentioned briefly in the article titled \"Mount
> Wilson Astronomer Estimates Milky Way Ten Times Bigger Than Thought\".
> Their true significance will be realized in the 1929 issue of the
> Cosmic Times. Leavitt discovered that the Cepheid variables she looked
> at in the Small Magellanic Cloud (a companion galaxy to our own) had a
> remarkable and predictable relationship between their period (the time
> it took to cycle once from bright to dim back to bright) and their
> luminosity. This might not be remarkable, except that since they were
> all part of the Small Magellanic Cloud, they could be considered to be
> at approximately the same distance. This, in turn, meant that the
> relationship was intrinsic to the stars and not a trick of the eye.
> See the 1929 and 1955 issues for more on this relationship and its
> significance.

-   \"Spectroscopic Observations of Spiral Nebulae\" -- V. M. Slipher

> Vesto Slipher discovered, in 1912, that Andromeda, a spiral nebulae
> (which we now know is another galaxy) had a redshift, meaning that it
> had a velocity with respect to the Earth. He continued to measure the
> spectra of other spiral nebulae, and found that they had a net
> positive velocity. In other words, they had a net velocity *away* from
> the Earth.

-   \"The Relation of the System of Stars to the Spiral Nebulae\"
    -- G. F. Paddock

> As mentioned above, astronomers did not know that the spiral nebulae
> were galaxies separate from our how; however, some astronomers had
> speculated as much, but the evidence was scant. This research suggests
> another small piece of evidence in favor of the spiral nebulae as
> entities outside our galaxy. Slipher had found that the spiral nebulae
> had an average radial velocity of +400 km/sec. However, no other type
> of object in our galaxy had a radial velocity of over +50 km/sec. This
> was a huge discrepancy.

# 1929 Cosmic Times

This poster is the second edition of the *Cosmic Times*, and the
articles in this edition build on the concepts introduced in the 1919
edition. The headline story is that Edwin Hubble has discovered that the
Universe is expanding. The idea of an expanding Universe is contrary to
Einstein's assumption of a static Universe, and while Einstein was not
convinced of the veracity of Hubble's results, the astronomical
community generally accepted them. This discovery was built on a second
important discovery that the Milky Way is one of many galaxies in the
Universe. This settled a debate among astronomers, which Harlow Shapley
and Heber Curtis had expounded upon in a formal debate in 1920. This
edition also contains brief biographies of Edwin Hubble and his
assistant Milton Humason.

The language in the 1929 newspaper mimics the style of writing that
would have appeared in a real 1929 newspaper. Like 1919, the language
and sentence structure of this edition are more difficult than modern
newspapers. The poster mimics the newspapers of the time, however, we
have taken some creative license to make it more readable in a classroom
setting. Real newspapers of the time would have had 5-7 narrow columns
of small type.

![](media/image3.jpeg){width="3.5in" height="4.813194444444444in"}

**Summary of the Articles**

### Andromeda Nebula Lies Outside Milky Way Galaxy

Up until the early 1920's, astronomers did not have definitive proof
that galaxies existed outside our Milky Way Galaxy. It was through the
use of Cepheid variable stars and the 100-inch telescope at Mt. Wilson
that Edwin Hubble determined the distance to Andromeda, and found it to
be outside our own Galaxy.

### Universe is Expanding

This article describes Edwin Hubble's discovery of that the universe is
expanding. Hubble put together his distances to the spiral nebulae with
the redshifts measured in their spectra. The linear relationship between
these two quantities showed that the Universe is expanding.

### "Great Debate" Resolved

Hubble's measurement of the distance to the Andromeda Nebula settled a
debate that had long raged among astronomers. This article reviews both
sides of this issue that were brought to light in a debate staged
between Harlow Shapley and Heber Curtis in April 1920.

### The Minds atop Mount Wilson

The story of science is as much about the scientists involved as it is
about the science itself. These two brief biographies highlight the
different lives of two of the astronomers who shaped our understanding
of the Universe in the early 20th century.

### Classifying Nebulae

The first step to understanding many different phenomena can often be to
classify them. To this end, Hubble looked at a large sample of galaxy
images and classified them according to their features. The general
classifications he used were: spiral, elliptical and irregular.

### In Their Own Words

This quote from Edwin Hubble is from an article in the Fresno Bee, which
appeared Oct 23, 1927, and offers his own perspective on his
discoveries.

## Notes on the 1929 Articles

### 

### Andromeda Nebula Lies Outside Milky Way Galaxy

*The primary message of this article is that until 1924, astronomers did
not know that the Milky Way Galaxy was just one of many galaxies in our
Universe. A secondary message is that determining distances to the stars
in other galaxies was only possible due to improvements in technology
and due to the discovery, by Henrietta Leavitt, of the period-luminosity
relationship of Cepheid variable stars.*

During the time of the 1919 Cosmic Times, astronomers did not have
definitive proof that galaxies existed outside our Milky Way Galaxy.
Observers had seen fuzzy patches in the sky, but they could not resolve
them into anything more than fuzzy patches. Without further evidence,
astronomers could only call these regions \"nebulae\", which was
generally associated with a cloud of gas and dust in space. The notes on
the article titled *\"Great Debate\" Resolved* talk a little more about
these nebulae and what astronomers thought they were. Here we\'ll talk
more about how Hubble revealed the true nature of some of these nebulae.

#### Standard Candles

Since astronomers cannot simply pull out giant measuring sticks to
determine distances to objects in the Universe, \"standard candles\"
have become a holy grail of sorts for studying the Universe. A standard
candle is any object that has a known brightness. With a known
brightness, astronomers can then infer a distance based on the observed
brightness of the object and the 1/r^2^ law.

#### Cepheid variables

In the early 1900s, Harvard astronomers employed women as "computers".
They took on tedious tasks such as determining the brightness of stars
on photographic plates and searching photographic plates for variable
stars.

Henrietta Leavitt was tasked with searching for variable stars in
photographic plates taken between 1893 and 1906 at Harvard College's
observatory in Peru. In 1908 she published a catalog of over 1777
variable stars. For 16 of these stars, she was able to measure a period
for their variability, and she noticed that the brighter stars of this
sample had longer periods.

By 1912, Leavitt had determined the period for a total of 25 variable
stars. She saw that the relationship she had observed in her 1908
catalog held up with these 25 stars. In fact, since all of the stars
were in the Small Magellanic Cloud, they could be considered to all be
at nearly the same distance. Given that, the relationship between their
period and luminosity was intrinsic to the stars, and not just a trick
of viewing stars at different distances.

These stars showed a similarity to another known variable star called
Delta Cepheid (the fourth brightest star in the constellation of
Cepheus), so they are collectively called Cepheid variables.

The one thing that Leavitt was missing was a distance to these Cepheid
variables in her sample. She had a period-luminosity relationship, but
no \"zero point\" for that relationship. It needed to be calibrated
against something with a known distance.

#### Calibrating the Cepheid scale

Ejnar Hertzsprung was the first person to try and calibrate the
period-luminosity scale for Cepheid variables. Using his calibration, he
came up with a distance to the Small Magellanic Cloud of 30,000 light
years (actually, the published value was 3,000 light years, but is
believed to be a typo which Hertzsprung either did not catch or did not
correct for some reason).

The next attempt to calibrate the Cepheid scale came with Harlow Shapley
in 1918. Shapley included \"Cepheids\" from globular clusters in his
calibration of the period-luminosity relationship, which will become
important in the next issue of the Cosmic Times. It was this calibration
of the relationship that Hubble used when he observed Cepheid variables
in the Andromeda Nebula.

#### Observing Andromeda

In 1924, Hubble was able to resolve the spiral arms of the Andromeda
Nebula into stars. Some of the stars that Hubble resolved were Cepheid
variables, for which Hubble was able to determine periods. Armed with
these periods and the calibrated period-luminosity relationship from
Shapely, Hubble was able to estimate the distance to Andromeda, and
found that it was 860,000 light years away -- further than the furthest
measured stars. At the time, the Milky Way was estimated to be about
300,000 light years, which we now know to be a huge overestimate, but
even with such an overestimate of the Milky Way\'s size, Andromeda was
far beyond the boundary.

Interestingly, even though Andromeda is generally thought to be the
first definitive observation of a star system far outside the Milky Way,
Hubble actually published results on NGC 6822 first. NGC 6822 is an
irregular galaxy that Hubble estimated to be about 700,000 light years
away, also very well outside Shapley\'s estimated size of the Milky Way.
It is thought that this result got very little attention because Hubble
had already published preliminary results for the spiral nebulae, so the
astronomical community generally agreed that there were other galaxies
in the Universe.

#### Other resources

The following web pages have more detailed information on the women
computers and the Cepheid distance scale:

-   [The Cepheid Distance Scale: A
    History](../../../../../../../../cgi-bin/leaving.pl%3Fhttp://www.institute-of-brilliant-failures.com/index.htm):
    http://www.institute-of-brilliant-failures.com/index.htm

-   [The Harvard Computers: From Pickering\'s Harem to Astronomy\'s
    Stars](../../../../../../../../cgi-bin/leaving.pl%3Fhttp://www.womanastronomer.com/harvard_computers.htm):
    http://www.womanastronomer.com/harvard_computers.htm

-   [Pickering\'s
    Harem](../../../../../../../../cgi-bin/leaving.pl%3Fhttp://cfa-www.harvard.edu/~jshaw/pick.html):
    http://cfa-www.harvard.edu/\~jshaw/pick.html

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Universe is Expanding

*The primary message of this article is that the Universe is expanding,
as shown by a linear relationship between the distance of a galaxy and
the velocity at which is receding discovered by Edwin Hubble. A
secondary message is that the cosmological constant, which Einstein
added to his equations of General Relativity to account for a static
Universe, may not be necessary, showing that even Einstein can be wrong
occasionally.*

This article introduces the idea of an expanding Universe. When we left
the Cosmic Times in 1919, Albert Einstein had added the Cosmological
Constant to his equations of General Relativity to prevent the Universe
from expanding. The idea of an expanding Universe was against his
philosophical viewpoint, and adding this Cosmological Constant to his
equations violated nothing.

#### Redshift

One key concept to understanding Hubble\'s results is understanding the
idea of redshift. Often this idea is introduced alongside the Doppler
effect for sound because students are much more familiar with this -- it
is what causes the pitch of a siren to appear to drop as it passes by a
listener. For light, when a source is emitting light while it is moving
away from us, the wavelength of the light as we see it will be shifted
toward the red, or toward longer wavelengths.

When astronomers look at light from distant galaxies, they can identify
signatures of certain elements in the form of \"spectral lines\". By
looking at how much these signatures are offset from their \"at rest\"
wavelengths, astronomers can tell how fast the object that emitted them
was moving. If the object is moving away from the observer, the light is
shifted toward the red, or toward longer wavelengths, and this is often
called \"redshift\". If the object is moving toward the observer, the
light is shifted toward the blue, which is often called \"blueshift\".

In 1917, an astronomer named Vesto Slipher discovered that the light
from several \"nebulae\" (later found to be galaxies) was
\"redshifted\". It is commonly thought that Hubble discovered the
redshift of galaxies, but this is not true. Hubble found the
relationship between redshift and distance that is discussed in this
Cosmic Times article, but he was not the first to see the redshift
itself.

#### Distance

The thing that Hubble added to the picture was determining both the
distance and redshift of galaxies. The distance determination was made
using a standard candle, called Cepheid variables. The importance of
these stars and how they are used in distance determinations are
discussed in more detail in the notes for the *Andromeda Nebula Lies
Outside Milky Way Galaxy* article.

#### Expanding Universe!

When Hubble plotted up the distance of the galaxies in his sample versus
the redshift of those galaxies, he found that there was a trend -- the
further a galaxy was, the faster it was moving away. This is exactly
what would be expected if the Universe was expanding.

This is one concept that your students might struggle with -- why does
an expanding Universe imply that the further a galaxy is from us, the
fast it would be moving away from us. To help illustrate this, imagine
that this picture shows several galaxies in the Universe as they were in
the past:

  -----------------------------------------------------------------------
  ![](media/image4.png){width="1.2340277777777777in"
  height="1.1222222222222222in"}

  -----------------------------------------------------------------------

Let\'s say that our galaxy is the blue star near the middle of the
picture. Then let the Universe expand for a while and look at what\'s
happened:

  -----------------------------------------------------------------------
  ![](media/image5.png){width="2.3006944444444444in"
  height="2.0993055555555555in"}

  -----------------------------------------------------------------------

We are the blue galaxy, so we haven\'t moved. However, all of the other
galaxies appear to have moved *away from us*. And, if you examine the
size of the arrows from the original galaxy positions to the new ones,
it is clear that the further a galaxy was away from us, the faster it
appears to have moved, *in the same amount of time*. That means that the
further away the galaxy was, the faster it appears to move away from us
as the Universe expands.

One misconception that your students may have is that because all of the
galaxies appear to be moving away from us that mean that we must be the
center of the Universe. This is not true. Any galaxy would actually
perceive the same thing. Let\'s say that instead of being the blue
galaxy in that image above that we are the yellow galaxy. The picture we
would see after the expansion would then be this:

  -----------------------------------------------------------------------
  ![](media/image6.png){width="2.2888888888888888in"
  height="2.0993055555555555in"}

  -----------------------------------------------------------------------

The yellow galaxy also sees all of the other galaxies moving away from
it, and the further the galaxy started from the yellow galaxy, the more
it moved.

The fact that we see the galaxies all moving away from us is indicative
of the expanding Universe, but *not* that we are the center of the
Universe. In fact, the expansion happens *everywhere*.

#### Einstein still didn\'t believe

If you read the 1919 edition of the Cosmic Times, you know that Einstein
did not like the idea of an expanding Universe. In fact, even though his
equations of General Relatively suggested an expanding Universe,
Einstein added his \"Cosmological Constant\" to those equations to
prevent expansion.

As of the publication date of this edition of the Cosmic Times, Einstein
is still not convinced of Hubble\'s results. However, in 1930, Einstein
travels to Mount Wilson to talk with Hubble and see his work first-hand.
After meeting with Hubble, Einstein does become convinced that the
Universe is, indeed, expanding.

#### Hubble\'s work holds up

Hubble\'s results have proved to hold over much greater distances than
Hubble himself could probe. As we\'ve developed larger and more
sensitive telescopes and as we\'ve determined more ways to pinpoint
distances in further and further objects, we have continued to find that
the further a galaxy is from us, the faster it is moving away, as this
image shows for just a sample of the currently available data:

  -----------------------------------------------------------------------
  ![](media/image7.png){width="5.298611111111111in"
  height="3.9270833333333335in"}

  The relationship between a galaxy\'s distance and its speed holds far
  beyond what Hubble originally measured. This diagram uses modern
  measurements to show the same relationship. The gray box shows the
  region that Hubble probed. Data from the Hubble Space Telescope Key
  project, courtesy Prof. John Huchra.
  -----------------------------------------------------------------------

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Sidebar: \"Great Debate\" Resolved

*The primary message of this article is that theories in astronomy, as
any other science, are based on evidence. When there are two leading
theories for the same phenomenon, astronomers must look objectively at
the available evidence for both theories to determine which is more
plausible. A secondary message is that science knowledge changes over
time when new evidence comes to light.*

Prior to Hubble\'s measurement of the distance to the Andromeda Nebula,
the nature of \"spiral nebulae\" was not definitively known. By 1920,
there was a growing number of scientists who believed that the spiral
nebulae were actually systems of stars outside our own galaxy, which
could not be resolved because of their great distances. However, other
scientists still believed that these spiral nebulae were clouds of gas
within the Milky Way.

To shed light on this debate in the astronomical community, two
astronomers on either side of this issue -- Harlow Shapley and Heber
Curtis -- held a debate on April 26, 1920 at the Smithsonian Museum of
Natural History.

Shapley argued that the whole of the Universe was contained in the Milky
Way, which was about 300,000 light years in size. The spiral nebulae
were clouds of gas held within the Milky Way galaxy. One theory about
the spiral nebulae was that they were solar systems in the process of
forming. In addition, astronomer Adriaan van Maanen claimed to have
observed rotation in the spiral nebulae. Shapley argued that the speeds
for such rotation would have to be too high if the nebulae were outside
the Milky Way. (Note: this claim of observed rotation in the spiral
nebulae is certainly wrong, though at the time it was an accepted
observation.)

Curtis argued that the Sun was part of a smaller system of stars
measuring about 30,000 light years across. He believed that the spiral
nebulae were *island universes* -- systems of stars external to our own
Milky Way. He demonstrated that the spectrum from these spiral nebulae
were indistinguishable from the spectrum from the Milky Way, suggesting
that they are similar in nature.

It was generally accepted that Shapley had won the debate with more
observations supporting his claims. However, we now know that Curtis was
correct on the nature of spiral nebulae. As technologies and
observations improve, our understanding of the Universe around us also
improves.

#### Other resources

The following web pages have more information on \"The Great Debate\":

-   [The Shapley-Curtis Debate - What is our Place in the
    Universe?](../../../../../../../../cgi-bin/leaving.pl%3Fhttp://astronomy.nmsu.edu/nicole/teaching/ASTR110/lectures/lecture27/slide01.html):
    http://astronomy.nmsu.edu/nicole/teaching/ASTR110/lectures/lecture27/slide01.html

-   [The Scale of the
    Universe](http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate20.html):
    http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate20.html

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### The Minds atop Mount Wilson

*The primary message of this article is that the story of science is as
much about the scientists involved as it is about the science itself.
The stories of Hubble and Humason show that there are many different
roads to a science career.*

The story of science is as much about the scientists involved as it is
about the science itself. These two brief biographies highlight the
unusual lives of two of the astronomers who helped to shape our
understanding of the Universe in the early 20^th^ century.

Edwin Hubble was a PhD astronomer with a wide range of interests from
Roman law to water polo to astronomy. Milton Humason, on the other hand,
dropped out of school when he was in eighth grade. Yet, both of these
men have their names connected to one of the seminal discoveries about
our Universe -- the Universe is expanding.

There are lots of interesting characters in science, from the well known
to the unknown, from Einstein to the women computers in \"Pickering\'s
Harem\".

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Sidebar: Classifying Nebulae

*The primary message of this article is that often the first step to
understanding many different phenomena can be to classify them.*

The first step to understanding many different phenomena can often be to
classify them. To this end, Hubble looked at a large sample of galaxy
images and classified them according to their features. The general
classifications he used were: spiral, elliptical and irregular. However,
each main classification also had sub-classes based on other
similarities.

Hubble\'s classification is often depicted in a diagram called the
\"Hubble Tuning Fork\". Hubble proposed that this classification scheme
may have been an evolutionary sequence for galaxies -- that galaxies may
evolve from one type to another throughout their lifetimes. Today, this
classification scheme is viewed as overly simplistic and the evolution
of galaxies is far more complex. However, Hubble\'s classifications were
the first step in understanding galaxy formation and structure, and the
classifications are often still used to describe galaxies.

  -----------------------------------------------------------------------
  ![](media/image8.jpeg){width="4.093055555555556in"
  height="3.359722222222222in"}

  Illustration of Hubble\'s classification scheme, often called the
  Hubble Tuning Fork. More information available here:
  http://hubblesite.org/newscenter/archive/releases/1999/34/image/o/.\
  *Image credit: NASA*
  -----------------------------------------------------------------------

#### Spiral Galaxies

Perhaps the best-known type of galaxy is spiral galaxies. These include
those where the spiral arms are clearly visible, such as M 31 pictured
below:

  -----------------------------------------------------------------------
  ![](media/image9.jpeg){width="2.7777777777777777in"
  height="2.7777777777777777in"}

  This is a composite image of the \"grand-design\" spiral galaxy M 81.
  More information available here:
  http://hubblesite.org/newscenter/archive/releases/2007/19/.\
  *Image credit: Hubble data: NASA, ESA, and A. Zezas
  (Harvard-Smithsonian Center for Astrophysics); GALEX data: NASA,
  JPL-Caltech, GALEX Team, J. Huchra et al. (Harvard-Smithsonian Center
  for Astrophysics); Spitzer data: NASA/JPL/Caltech/Harvard-Smithsonian
  Center for Astrophysics.*
  -----------------------------------------------------------------------

However, spirals encompass a larger range than just those for which we
can see the spiral arms. One way to think of a spiral type galaxy is a
galaxy with a central bulge and a disk. The spiral arms are contained
within the disk of the galaxy. If we observe such a galaxy edge-on, we
don\'t see the spiral arms. Here is an example of an edge-on spiral
galaxy:

  -----------------------------------------------------------------------
  ![](media/image10.jpeg){width="2.7777777777777777in"
  height="2.7777777777777777in"}

  The Sombrero Galaxy is a spiral galaxy where we are observing the disk
  edge-on. The dark line through the galaxy is actually the disk. More
  information available here:
  http://hubblesite.org/newscenter/archive/releases/2003/28/.\
  *Image Credit: NASA and The Hubble Heritage Team (STScI/AURA).*
  -----------------------------------------------------------------------

In addition, about half of the spiral galaxies have a bar-like structure
in the central bulge of the galaxy.

  -----------------------------------------------------------------------
  ![](media/image11.jpeg){width="2.7777777777777777in"
  height="1.6527777777777777in"}

  NGC 1300 is a classic example of a spiral galaxy with a \"bar\" in the
  central bulge. More information available here:
  http://hubblesite.org/newscenter/archive/releases/2005/01/.\
  *Image Credit: Credit: NASA, ESA, and The Hubble Heritage Team
  (STScI/AURA)*
  -----------------------------------------------------------------------

Hubble sub-classified spiral galaxies based on a combination of how
tightly the spiral arms appeared to be wrapped around the bulge and the
relative size of the bulge compared to the disk. Type Sa galaxies
(spiral, sub-type a) have large bulges and are tightly wrapped, while
type Sc galaxies have small bulges and loosely wrapped arms. The barred
spiral galaxies are similarly sub-classified.

#### Ellipticals

Elliptical galaxies are those that appear, well, elliptical. The shape
of an elliptical galaxy can appear to be anywhere from perfectly round
to cigar shaped. Hubble sub-classified elliptical galaxies based on
their \"ellipticity,\" which is defined as 10 times the eccentricity.
Or:

$\text{ellipticity} = \text{10}´\frac{\text{major}\text{axis} - \text{ min}\text{or}\text{axis}}{\text{major}\text{axis}}$

  ------------------------------------------------------ ---------------------------------------
  ![](media/image12.jpeg){width="3.1479166666666667in"   ![](media/image13.jpeg){width="2.4in"
  height="2.3583333333333334in"}                         height="2.4in"}

  Two types of elliptical galaxies. The image on the     
  left is M 87, an elliptical that appears nearly        
  circular and is classified as an E0 galaxy in the      
  Hubble classification scheme. The image on the right   
  is M 101, an elliptical that appears more elongated    
  and is classified as an E5 galaxy in the Hubble        
  classification scheme.\                                
  *Image credits: Both images are from Jarrett et al.,   
  Astronomical Journal 125, 525 (2003).*                 
  ------------------------------------------------------ ---------------------------------------

It should be noted that the apparent shape of an elliptical galaxy in
the sky is more dependent on our line-of-sight to that galaxy than any
intrinsic properties of the galaxy itself. If a galaxy were
intrinsically cigar shaped, and we viewed it edge-on, it would appear
circular.

#### Irregular Galaxies

Hubble found that not all galaxies fell neatly into the \"spiral\" or
\"elliptical\" categories. They don\'t show obvious spiral structure,
nor do they show a central bulge, so they are not spiral galaxies. In
addition, they lack symmetry, so are not elliptical galaxies. These hard
to classify galaxies were lumped into a separate category -- irregular
galaxies.

  ---------------------------------------------------------------------------------------
  ![](media/image14.jpeg){width="2.7777777777777777in" height="3.138888888888889in"}

  NGC 1427A is an example of an irregular galaxy. It does not have any hint of spiral
  structure, a bulge or symmetry. In fact, this image, from the Hubble Space Telescope,
  shows that this galaxy is falling headlong into the Fornax galaxy cluster, and will not
  survive long as a recognizable galaxy. More information available here:
  http://hubblesite.org/newscenter/archive/releases/galaxy/irregular/2005/09/image/a/.\
  *Image credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA).*
  ---------------------------------------------------------------------------------------

#### Additional Resources

-   [Galaxy Classification
    Activity](../../../../../../../../cgi-bin/leaving.pl%3Fhttp://www.astro.lsa.umich.edu/undergrad/Labs/GalClass/GalClassShort.html):
    http://www.astro.lsa.umich.edu/undergrad/Labs/GalClass/GalClassShort.html

-   [Galaxy
    Classification](../../../../../../../../cgi-bin/leaving.pl%3Fhttp://www.astr.ua.edu/keel/galaxies/classify.html):
    http://www.astr.ua.edu/keel/galaxies/classify.html

# 1955 Cosmic Times

This poster is the third edition of the *Cosmic Times*, dated to
coincide with Einstein's passing. Much has happened since 1929, with
developments in previous stories and completely new discoveries.
Astronomers discovered there were two populations of Cepheid variables,
leading to a re-calibration in the use of the Cepheids as standard
candles and a doubling of the size of the Universe. A debate raged
between whether the Big Bang or the Steady State theory correctly
described the origin and nature of the Universe. Also, astronomers not
only recognized the distinction between novae and supernovae, but there
different types of supernovae. Finally, astronomers get their first
"glimpse" of objects emitting in a region of the electromagnetic
spectrum other than optical light.

The language in the 1955 newspaper mimics the style of writing that
would have appeared in a newspaper at that time. While this is getting
closer to familiar language and sentence structure of modern newspapers,
it may still be a bit difficult for students to read. The poster also
shows a layout that mimics the papers of the time. However, we have
taken some creative license to make it more readable in a classroom
setting.

![](media/image15.jpeg){width="3.5in" height="4.813194444444444in"}

**Summary of the Articles**

### 

###  'Yardsticks' in Neighbor Galaxy Double Universe's Size

This article describes how astronomers discovered a miscalibration in
the Cepheid distance scale. This arose from the discovery of the
existence of two populations of Cepheids with two different
period-luminosity relationships. When this miscalibration was corrected,
the size of the Universe doubled overnight.

### Origin of Everything

As of 1955, there were two equally likely theories for the origin of the
Universe -- the steady-state theory and the evolutionary Universe theory
(later known as Big Bang theory). Although predictions were made by both
theories, at the time, the observational evidence was insufficient to
decide between them.

### Hoyle Scoffs at "Big Bang" Universe Theory

Ironically, the biggest detractor of the evolutionary Universe theory
ended up coining the phrase by which it is became to be known -- the Big
Bang. Hence, everyone seems to contribute to the progress of science!

### Death of a Genius: Albert Einstein 1879 - 1955

This article shows how Einstein's death was felt the whole world over.

### It's a Star! It's a Nova! It's Super-nova

This article begins the important story of supernovae by picking up with
the discovery made that these stellar explosions can be classified into
two types: novae and super-novae. Further, these super-novae can be
split up into two different kinds -- Type I which show no signs of
hydrogen in their spectrum and Type II which do show hydrogen.

### Radio 'Ear' on the Universe Being Built

By the mid-1950s technologies inherited from World War II allowed
astronomers to look at radio waves emitted by objects in the Solar
System and beyond. Hence astronomy was no longer confined to the realm
of optical observations.

## Notes on the 1955 Articles

### 

### \"Yardsticks\" in Neighbor Galaxy Double Universe\'s Size

*The primary message of this article is that a miscalibration of the
Cepheid distance scale, stemming from the existence of two populations
of Cepheids with two different period-luminosity relationships, resulted
in an underestimation of distances in the Universe. When this
miscalibration was corrected, the size of the Universe doubled
overnight.*

Before we discuss the problem with the Cepheid variable distance scale
that was discovered in the 1940s, researchers had already seen evidence
of a problem with the distance scale. Astronomers are always looking for
different types of \"standard candles\" -- objects of known brightness
for which a distance can then be calculated using the observed
brightness. One such object that astronomers tried to use in the early
days of extra-galactic observations was the globular clusters of a
galaxy. Globular clusters are a type of star cluster that tend to lie in
the halo of a galaxy. In 1931, Hubble compared the brightest globular
cluster in our galaxy to the brightest one in Andromeda, and found that
the one in Andromeda was intrinsically much dimmer than the one in ours.

Later, he compared the globular clusters in our galaxy to those in
Messier 33 (M 33), another spiral galaxy that is further than Andromeda.
He found that the globular clusters in M 33 were still fainter than
those in Andromeda, based on the distances he had earlier found. Hubble
recognized that it was possible for globular clusters to vary from
galaxy to galaxy, but it seemed unlikely that they would preferentially
get dimmer the further they were from our galaxy. This pointed to a
problem with the distance scale, but Hubble did not have an explanation
for the origin of the problem.

When Baade discovered that there were, in fact, two different
populations of stars, it did not take researchers long to connect the
dots between the discrepancy that Hubble was seeing in the globular
clusters of distant galaxies and the Cepheid distance scale. Baade\'s
images of Andromeda and Andromeda\'s two companion galaxies, Messier 32
and NGC 205, showed that there were two populations of stars, which he
called \"Type I\" and \"Type II\" -- Type I stars were bluer and
brighter whereas the Type II were redder and fainter. He recognized that
the globular clusters were rife with Type II stars, whereas the disk of
the galaxies tended to have both Type I and II stars.

As it happens, the Large Magellanic Cloud, the location of the Cepheid
variables that Henrietta Leavitt observed, is populated with Type I
stars. However, when Shapley calibrated the Cepheid period-luminosity
relationship, he was using observations of Cepheid variables in globular
clusters -- where Type II stars reign. The Cepheid variables that Hubble
observed in the Andromeda nebula were Type I, but he unknowingly used
Shapley\'s calibration that were calibrated for Type IIs. The problem
lies in the fact that there are two different calibrations of the
period-luminosity for the two different populations of Cepheid
variables.

The re-calibration of the Cepheid scale for the Type I Cepheids showed
that the distances to the Type I Cepheids was off by about a factor of
2. In other words, astronomers were finding distances that were half as
far as they should have been. Andromeda suddenly went from being a
\"mere\" 800,000 light-years away to being about 1,800,000 light-years
away. With this new distance, the brightest globular clusters in
Andromeda were now about the same intrinsic brightness as those found in
our own galaxy.

To bring this discussion into a more modern note, astronomers have
studied the differences between Type I and Type II stars in more detail.
Typically, these are now referred to as Population I and Population II
instead of Type I and Type II. Astronomers have found that one
difference between Population I and II stars it the amount of heavy
elements in the stars. Population II stars show very little heavy
elements where Population I have more. It is thought that Population II
stars are, therefore, older stars, formed earlier in our Universe\'s
lifetime. This is because the Universe started as mainly hydrogen and
helium. This is still true, but the abundances of the elements heaver
that hydrogen and helium have slowly increased as stars fuse hydrogen
into heavier and heavier elements. Population I stars were likely formed
out of the remains of earlier, Population II stars.

#### Other resources

The following web page has additional information:

-   [Characteristics of
    Galaxies](http://imagine.gsfc.nasa.gov/docs/teachers/galaxies/imagine/characteristics.html):
    http://imagine.gsfc.nasa.gov/docs/teachers/galaxies/imagine/characteristics.html

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Origin of Everything: Hot Bang or Ageless Universe?

*The primary message of this article is that as of 1955, there were two
equally probable theories for the origin of the Universe -- the
steady-state theory and the evolutionary Universe theory (later known as
Big Bang theory). At the time, the observational evidence was
insufficient to decide between the two theories.*

In the 1950s there were two theories regarding the nature of the
universe: the Steady State and the Big Bang. At that time, there was not
sufficient observational evidence to clearly favor or disprove either of
them.

The British astronomer Fred Hoyle was the champion of the Steady State
theory. He, Tommy Gold, and Hermann Bondi developed this theory after
seeing the movie *Dead of Night*, which ends the way it begins. Hoyle
thought that the universe could be unchanging but dynamic. So as the
universe expands, matter is created to fill the space. It would require
only 1 hydrogen atom per cubic meter every 300,000 years (comparable to
\"a few hundred atoms per year per galaxy\"). Hoyle developed the
\"Perfect Cosmological Principle\", which states that the universe is
the same at any place and at any time.

The \"Evolutionary\" model for the universe (a.k.a. \"Big Bang\") was
built on theoretical work in the 1920s and 1930s. In the 1940s, George
Gamow was trying to solve the problem of the origin of the chemical
elements. He determined that most elements could not form in the early
universe - the right conditions of temperature and density would not
last long enough. With Alpher, he showed that hydrogen and helium would
form (and in the right proportions), but nothing heavier. (Later
astronomers figured out how heavier elements could be made in the dense
hot core of stars.). In doing this, Gamow developed many of the
fundamental ideas about the early \"evolutionary\" universe. He
developed the relation between temperature and mass density, recognized
that atoms (not just nuclei) would form only after the universe had
cooled sufficiently, and developed the theory of early galaxy formation.
In 1949 Alpher and Herman redid these calculations, and in doing so
predicted a \"relic primordial radiation\" with a temperature of about 5
K. They didn\'t think this would be detectable, and indeed instruments
at the time could only detect a background radiation of only 20 K.

Both theories made predictions. Some are described in the table below

  -----------------------------------------------------------------------
  Issue            Steady State           Big Bang
  ---------------- ---------------------- -------------------------------
  Density of the   The density is         The density changes, but do
  Universe         constant               known physical laws apply at
                                          early time of very high
                                          density?

  Age of the       Ageless                In 1955, Big Bang gave an age
  Universe                                less than known age of solar
                                          system

  Rate of          Expansion is constant  Expansion should slow
  Expansion                               

  Ages of Galaxies Old and young Galaxies Galaxies age with time
                   should be mixed in     
                   space                  

  Background       There should be none   It should exist, with a
  Microwave                               temperature of about 5 K
  Radiation                               
  -----------------------------------------------------------------------

In the 1950s, the evidence was mixed. A number of observations seemed to
favor the Big Bang, but it was not definitive. The fact that the age
derived for the Big Bang was less than the known age of the Solar System
was a major problem. However, there was no conclusive evidence for one
theory or the other.

Interestingly, the presence of the Steady State as a competing theory
provided the impetus to make the observations to test the theories.

#### Side Notes:

-   Interestingly, one of Thomas Bondi\'s major contributions to
    astronomy came with the discovery of pulsars in 1967. He was the
    first to explain them as rotating neutron stars, which turned out to
    be correct.

-   As a bit of joke, Gamow asked Hans Bethe if his name could be
    included on the paper Gamow was writing with Alpher. Bethe, who had
    not participated at all in the research, agreed. So the initial
    paper on the Big Bang was authored by Alpher, Bethe and Gamow,
    reminiscent of the first three letters of the Greek alphabet, Alpha,
    Beta, and Gamma.

-   Alpher was Gamow\'s graduate student, and only after many years did
    he get full credit for working out Gamow\'s ideas, and predicting
    the cosmic microwave background. In the mid-1950\'s Alpher and
    Herman\'s theories were challenged by supporters of the Steady
    State. Alpher and Herman were nearly forgotten when Penzias and
    Wilson discovered the cosmic microwave background in 1965 (although
    Penzias mentioned their work in his Nobel lecture in 1978). Alpher
    received honors starting in the 1970\'s culminating with the
    National Medal of Science (the highest scientific honor in the US)
    two weeks before he died in 2007.

#### Other resources

The following web pages have more detailed information:

-   [Arno Penzias\' Nobel Prize
    Lecture](../../../../../../../../cgi-bin/leaving.pl%3Fhttp://nobelprize.org/nobel_prizes/physics/laureates/1978/penzias-lecture.html)
    : describes the development of the Big Bang theory and how
    astronomers wrestled with the problem of the origin of the chemical
    elements:
    http://nobelprize.org/nobel_prizes/physics/laureates/1978/penzias-lecture.html

-   [Big Bang or Steady
    State?](../../../../../../../../cgi-bin/leaving.pl%3Fhttp://www.aip.org/history/exhibits/cosmology/ideas/bigbang.htm) -
    an article from the American Institute of Physics describing the
    issues surrounding these two theories:
    http://www.aip.org/history/exhibits/cosmology/ideas/bigbang.htm

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Sidebar: Hoyle Scoffs at \"Big Bang\" Universe Theory

*The primary message of this article is that the biggest detractor of
the evolutionary Universe theory ended up coining the phrase by which it
is became to be known -- Big Bang theory.*

Hoyle was no fan of the \"evolutionary\" model of the universe. He
coined the term \"Big Bang\" on a BBC radio broadcast of *The Nature of
Things* in 1949. The term took about another decade to really catch on.
Once it did, however, the term stuck. Attempts have been made to rename
it, since it mistakenly leaves the impression that the universe started
with an explosion. For example, in 1993 Sky and Telescope magazine ran a
contest to rename it, and received many interesting ideas. More
amusingly (but still perpetuating the explosion misconception), Bill
Watterson in his *Calvin and Hobbes* comic strip referred to it as \"The
Horrendous Space Kablooie!\"

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Death of a Genius: Albert Einstein 1879-1955

*The primary message of this article is that Einstein\'s death was felt
the whole world over.*

There were many obituaries and reminiscences when Einstein died, and
this brief article attempts to capture just a small portion of that.

Einstein spent the last thirty years of his life working on \"the theory
of everything\", which would attempt to unify gravity and quantum
mechanics. During those years, he was about the only person working on
the problem, and he did not succeed. However, that question is still
pursued today.

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### It\'s a Star! It\'s a Nova! It\'s Super-Nova!

*The primary message of this article is that stellar explosions can be
classified into two types: novae and super-novae. And that super-novae
can be split up into two different kinds -- Type I that show no signs of
hydrogen in their spectrum and Type II that do show hydrogen.*

Astronomers had long been observing new stars, or novae. These are newly
visible stars whose brightness changes by hundreds or millions of times
(increasing between 5 to 15 magnitudes). They had been observed in our
galaxy, and in the \"spiral nebulae\". Once Hubble determined the
distance to the Andromeda Nebula, he realized that the bright nova that
had been observed to have occurred there in 1885 must have been much
more luminous than those occurring in our own galaxy. By 1934 there was
growing evidence from other bright novae in distant galaxies that there
were two types of phenomena. Walter Baade and Fritz Zwicky were
apparently the first to coin the term \"super-nova\". Minkowski studied
the spectra from these supernovae and determined there were two types.

We now know novae to be an event that happens on a white dwarf. A white
dwarf is the remnant of a star like our sun after it has used all its
nuclear fuel. White dwarfs may be at the center of planetary nebulae, or
in orbit around another star. When in a close orbit around another star,
the white dwarf can accumulate matter from its companion. With enough
material on the surface of the white dwarf, there is an episode of
nuclear burning of the accumulated hydrogen. This happens rather
quickly, and the star brightens.

Supernovae are much more violent events, and hence much brighter.

-   Type Ia supernovae (a subclass of the Type Is discussed in the
    article) is the total destruction of a particular type of white
    dwarf. Here enough material accumulates on the white dwarf that it
    reaches the upper allowed limit of its mass, 1.4 times the mass of
    the sun (a limit discovered by Chandrasekhar). Once this limit is
    reached, carbon and oxygen in the core of the white dwarf fuse,
    completely detonating the star.

-   Type II supernovae result from massive stars that have come to the
    end of their lives. Stars that start with more than 8 times the mass
    of the sun go supernova when their cores start to fill with iron,
    the last step in a long chain of fusion processes. Since iron does
    not generate energy by nuclear fusion, the core collapses under its
    own weight. The rest of the star falls onto the collapsing core, and
    then bounces back, creating the supernova explosion. The energy of
    the explosion is enough to create heavy elements beyond iron. The
    explosion leaves behind a neutron star or a black hole (depending on
    the original mass), as well as a gaseous remnant (known as a
    supernova remnant).

#### Side Note

-   The style of this article plays off the popularity of Superman in
    the mid-1950s. The Superman comic books debuted in the 1930s, and
    were wildly popular by the early 1940s. In 1955, the television
    series \"Adventures of Superman\", starring George Reeves, was in
    its heyday.

#### Other resources

The following web pages have more detailed information:

-   [Supernovae](http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html) -
    basic information about supernovae:
    http://imagine.gsfc.nasa.gov/docs/science/know_l2/supernovae.html

-   [Supernovae](http://imagine.gsfc.nasa.gov/docs/science/know_l2/supernovae.html) -
    more information about supernovae:
    http://imagine.gsfc.nasa.gov/docs/science/know_l2/supernovae.html

-   [Teachers Guide to the Life Cycles of
    Stars](http://imagine.gsfc.nasa.gov/docs/teachers/lifecycles/LC_title.html):
    http://imagine.gsfc.nasa.gov/docs/teachers/lifecycles/LC_title.html

-   [\"What is Your Cosmic Connection to the
    Elements?\"](http://imagine.gsfc.nasa.gov/docs/teachers/elements/elements.html) -
    a teachers guide to the origin of the chemical elements, including a
    section on supernovae:
    http://imagine.gsfc.nasa.gov/docs/teachers/elements/elements.html

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Radio \'Ear\' on the Universe Being Built

*The primary message of this article is that astronomy is no longer
confined to the realm of optical observations -- new technologies allow
astronomers to look at radio waves emitted by objects in the Solar
System and beyond.*

Radio was the first non-optical portion of the electromagnetic spectrum
to be explored by astronomers. This article introduces students to this
fact, and that radio astronomy was flourishing in the 1950s. This
article sets the stage for the further expansion of astronomy into the
X-ray and microwave regions of the spectrum, which become quite
important in the 1965 and 1993 issues of Cosmic Times.

Radio astronomy had its origins in the early 1930s, when Karl Jansky was
investigating the sources of noise in a radiotelephone system at Bell
Telephone Labs in New Jersey. He linked the source of the noise to
something in the sky, rather than the immediate surroundings. He
identified the source to be the center of our Galaxy. Most astronomers
took little notice of this discovery. Grote Reber, a radio engineer and
amateur astronomer, learned of the discovery in 1933 and built his own
radio telescope. By the early 1940s Reber had made detailed maps of the
radio sky.

The impetuses for the advancement of radio astronomy were the
necessities and technological advances from World War II. The
necessities included classified work by the British to determine the
source of the jamming of British radars -- which turned out to be the
Sun. New receivers built for the War provided the basis for new radio
telescopes after the War. By the early 1950s, Martin Ryle and Antony
Hewish had started the Cambridge catalogues (\"2C\" and \"3C\") of radio
sources. By the mid 1950s, radio astronomy was flourishing.

Jodrell Bank, which is 25 miles south of Manchester, England, was first
used for radio astronomy when Bernard Lovell brought surplus WW II radio
equipment there in 1945. Jodrell Bank Observatory was expanded in 1952,
offering a place to build the Mark I telescope.

The Mark I telescope at Jodrell Bank was completed in 1957, and later
became known as the Lovell Telescope, named for the observatory\'s
founder. Shortly after its completion, it tracked the booster rocket
that carried Sputnik 1 into orbit. The Lovell Telescope remains the
third largest steerable radio telescope in the world.

The Lovell Telescope has been used to track a number of planetary
probes. It has been used extensively for astronomy research, including
the study of pulsars, star-forming regions, quasars, and gravitational
lenses.

In the Cosmic Times article, the \"brightest radio emitter \... in the
constellation Cassiopeia\" is Cassiopeia A, later found to be a
supernova remnant. Cassiopeia A is now extensively studied to understand
the nature of supernova explosions, formation of chemical elements, and
how the remnant interacts with the surrounding interstellar gas.

#### Other resources

The following web pages have more detailed information:

-   [Jodrell Bank Centre for
    Astrophysics](../../../../../../../../cgi-bin/leaving.pl%3Fhttp://www.jb.man.ac.uk/) -
    for current research done at Jodrell Bank and other radio
    observatories run by University of Manchester:
    http://www.jb.man.ac.uk/

-   [Lovell
    Telescope](../../../../../../../../cgi-bin/leaving.pl%3Fhttp://en.wikipedia.org/wiki/Lovell_Telescope) -
    Wikipedia article: http://en.wikipedia.org/wiki/Lovell_Telescope

-   [Jodrell Bank
    Observatory](../../../../../../../../cgi-bin/leaving.pl%3Fhttp://en.wikipedia.org/wiki/Jodrell_Bank_Observatory) -
    Wikipedia article:
    http://en.wikipedia.org/wiki/Jodrell_Bank_Observatory

-   [Cas A and Other Supernova
    Remnants](http://chandra.harvard.edu/xray_sources/supernovas6.html):
    http://chandra.harvard.edu/xray_sources/supernovas6.html

# 1965 Cosmic Times

This edition, the fourth of the series, *Cosmic Times*, coincides with
the discovery of the cosmic microwave background (CMB), the remnant
radiation from very early in the Universe. This new discovery clearly
makes the Big Bang the lead theory on the origin of the Universe. The
realm of astronomy has grown, with the addition of observations of
X-rays from outside the Solar System, and, indeed, outside of the
Galaxy. Astronomers have also just gotten their first glimpse of the
invisible dark matter.

The language in the 1965 newspaper mimics the style of writing that
would have appeared in a real 1965 newspaper. The style is very close to
modern-day newspapers, and should not be as difficult for your students
as previous papers. However, the concepts may be more difficult than in
the previous *Cosmic Times* editions. The layout of the poster also
mimics the newspapers of the time. However, we have taken some creative
license to make it more readable in a classroom setting.

![](media/image16.jpeg){width="3.5in" height="4.813194444444444in"}

**Summary of the 1965 Articles**

### 

### Murmur of a Bang

A pair of astronomers, Penzias and Wilson, stumbled upon the discovery
of the cosmic microwave background. This discovery played a pivotal role
in overthrowing the Steady State theory. This article shows that science
does not always take the expected route -- unexpected discoveries are
sometimes the richest discoveries.

### Big hiss missed by others

Other scientists had the potential to discover the cosmic microwave
background, but were not able to connect the observation and theory.

### Supernovae Leave Behind Cosmic X-ray Generators

Not all wavelengths of light are able to penetrate the Earth's
atmosphere, so astronomers must use satellites to expand astronomy
beyond optical and radio wavebands. This article reinforces the idea of
multiwavelength astronomy that was introduced in the 1955 Cosmic Times
article, *Radio 'Ear' on the Universe Being Built*.

### Quasars: Express Trains to the Netherworld

Astronomers have discovered objects near the edge of the known Universe
that appear to be speeding away from us due to the expansion of the
Universe. In addition, we see the shear power these objects must have if
we are able to observe them across such great distances.

### Galaxies Still Misbehaving

This article illustrates that there is mass in this universe that we
cannot account for by studying light alone. In fact, there isn't just a
little more matter, but a lot more. This article shows that we can
observe phenomena in our universe by their influences on other parts of
the universe -- in this case, we observe the presence of dark matter
through its affect on the motions of galaxies and galaxy clusters.

## Notes on the 1965 Articles

### 

### Murmur of a Bang

*The primary message of this article is the introduction of the cosmic
microwave background and its role in overthrowing the steady state
theory. A secondary message of this article is the idea that science
does not always take the expected route -- unexpected discoveries are
sometimes the richest discoveries.*

#### Serendipitous Discovery

The \"Holmdel horn\" had been built by Bell Labs to test
telecommunications with the Echo satellite, but was no longer needed for
that job as of mid-1962. With its primary task finished, the Holmdel
horn was made available to Arno Penzias for astronomical observations.
Robert Wilson was hired to help out.

To use the Holmdel horn for astronomical purposes, Penzias and Wilson
first needed to characterize the \"noise\" in the telescope. For
astronomers, \"noise\" refers to light that enters a telescope from a
source other than the object of study. Noise can come from many places,
such as the detector itself, nearby lights from a city, or sources in
the sky that lie close to the object of interest. By characterizing the
noise sources, astronomers can better determine the signal that came
from the object they wish to study. Astronomers must track the noise in
all astronomical instruments to be confident in their observations and
conclusions. For the Holmdel horn, Penzias and Wilson identified all
possible noise sources, including cleaning pigeon droppings from the
horn itself, but found they had remaining noise that they could not
trace.

As discussed in the article, *Big Hiss Missed by Others*, other
researchers had been looking for the remnant radiation from shortly
after the Big Bang. The Big Bang model was already the front-runner for
the model of our Universe, but finding the remnant radiation was seen as
the smoking gun that would effectively squash any other model (such as
the steady state model). It is interesting to note that Penzias and
Wilson were not among the researchers actively seeking out the remnant
radiation of the Big Bang.

While Penzias and Wilson were contemplating the possible remaining
source of noise, they heard about work done by Princeton researchers
Dicke and Peebles. Dicke sent them a draft of his group\'s paper on
radiation in the universe. The theoretical work by Dicke\'s group on the
remnant radiation from the Big Bang was just the thing that Penzias and
Wilson needed to pin down their extra \"noise\" source. The noise they
hadn\'t been able to characterize was not coming from any local sources
-- it was the Universe itself!

The two teams published their papers in the same volume of the
*Astrophysical Journal* in 1965:

-   \"Cosmic Black-Body Radiation\" by Dicke, Peebles, Roll, and
    Wilkinson, D. T. appeared in *Astrophysical Journal*, volume 142,
    pages 414-419 (1965)

-   \"A Measurement of Excess Antenna Temperature at 4080 Mc/s\" by
    Penzias and Wilson appeared in *Astrophysical Journal*, volume 142,
    pages 419-421 (1965)

#### Signature Radiation

The Cosmic Times article discusses how \"the remnants of the Big Bang
have cooled in a way that channels energy into specific bandwidths\".
This is our writer\'s way of saying that the remnant radiation has a
specific spectrum -- that of a black body. In fact, the black-body
spectrum of the remnant radiation was predicted by the theorists, and
was, indeed, what Penzias and Wilson saw in their \"noise\".

Black-body radiation has a specific spectrum. Black bodies radiate at
all wavelengths, but the spectrum has a peak at a wavelength where most
of the energy radiates. This peak wavelength (or energy) completely
characterizes the black-body spectrum. The remnant radiation from the
Big Bang peaks in the microwave range of the electromagnetic spectrum,
so it is now called the \"cosmic microwave background\" or CMB for
short.

  -----------------------------------------------------------------------
  ![](media/image17.png){width="5.173611111111111in"
  height="3.7555555555555555in"}

  Blackbody spectrum for several different characteristic temperatures.
  The 3K spectrum like that of the CMB is not shown on this plot.
  -----------------------------------------------------------------------

#### Significance of the Discovery

The discovery of the cosmic microwave background (CMB) was the final
straw for the steady-state model of the universe. The steady-state model
cannot account for the CMB without major backbreaking efforts. Most
scientists had already seen that the Big Bang model was the more
reasonable theory, with more hard evidence. With the discovery of the
CMB, however, all but a few die-hard hangers-on abandoned the steady
state theory.

This story illustrates two important processes in science -- first, the
idea that serendipitous observations often yield the most interesting
science, and second, that often one person\'s trash is another person\'s
treasure. Penzias and Wilson never intended to find the CMB -- they were
only hoping to use the Holmdel horn for astronomical purposes. In order
to do that, they needed to characterize all of the noise in the system.
The so-called noise, however, was a gem in the field of cosmology, and
has become the cornerstone for understanding the nature of the universe.

The CMB is so important, that studying and mapping it became the focus
of two NASA satellite missions. The results of the first mission are
discussed in the 1993 edition of Cosmic Times.

#### Other resources

The following web pages have more detailed information:

-   [Short autobiography of Arno Penzias on the Nobel Prize
    website](http://nobelprize.org/nobel_prizes/physics/laureates/1978/penzias-autobio.html):
    http://nobelprize.org/nobel_prizes/physics/laureates/1978/penzias-autobio.html

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Big hiss missed by others

*The primary message of this article is to point out that theory and
observation must both coordinate to advance our understanding of the
Universe. A secondary message is that not all discoveries are planned --
many of the richest discoveries happen by accident. It\'s one of the
things that keeps science fun!*

While the tools to find the echo of the Big Bang were known and could
have been found by others, it is no big surprise that other researchers
missed it. Theorists had been pursuing the cosmic microwave background
(CMB), but most believed that it would be too faint to be detected.

Another factor that made the CMB difficult to find was that some
theorists estimated a higher temperature for the CMB than was actually
found. As discussed in the notes for the article *Murmur of a Bang*, the
spectrum of light of the CMB is that of a black body. A black-body
spectrum is characterized by the wavelength at which it peaks,
corresponding to a characteristic temperature. Without knowing the
characteristic temperature of the CMB, the signal would be easy to miss.

Perhaps if Penzias and Wilson had not seen the paper by Dicke, they
would have written the excess noise off to some \"unattributable
source\", and continued with astronomical observations, oblivious to
cosmological gem they had at their fingertips.

And as a side-note, a few other things in science that were discovered
by accident include penicillin and gamma-ray bursts. It may be fun to
have students find other examples.

#### Other resources

The following web page has more detailed information:

-   [Cases of Accidental Scientific
    Discoveries](http://www.trivia-library.com/cases-of-accidental-scientific-discoveries/index.htm)
    at Trivia-Library.com:
    http://www.trivia-library.com/cases-of-accidental-scientific-discoveries/index.htm

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Supernovae Leave Behind Cosmic X-ray Generators

*The primary message of this article is that astronomer need to put
telescopes in orbit in order to study the wavelengths that don\'t pass
through the Earth\'s atmosphere. This article also reinforces the idea
of multiwavelength astronomy that was introduced in the 1955 Cosmic
Times article, \"Radio \'Ear\' on the Universe Being Built\".*

For thousands of years, the only form of astronomy observation was
optical observation -- the light we could see with our eyes. All
telescopes, lenses and cameras were sensitive only to optical light. The
20^th^ century saw the advent of astronomy in other wavelengths. Radio
astronomy began in the 1930s (as we found in the 1955 Cosmic Times
article titled *Radio \'Ear\' on the Universe Being Built*), with the
first sky-survey in radio wavelengths conducted in the 1950s. The
subject of the main 1965 article, *Murmur of a Bang* describing the
discovery by Penzias and Wilson of the cosmic microwave background, was
done with an antenna sensitive to microwave wavelengths.

There is a limit, though, to the portions of the electromagnetic
spectrum that can be studied from the Earth\'s surface. Earth\'s
atmosphere stops many wavelengths of light from reaching the Earth\'s
surface -- lucky for us, because many of these wavelengths are harmful
to humans. However, this means that for the wavelengths stopped by the
atmosphere, observations must take place above the atmosphere.

  -----------------------------------------------------------------------
  ![](media/image18.jpeg){width="2.0in" height="2.9652777777777777in"}

  A sounding rocket
  -----------------------------------------------------------------------

X-ray wavelengths are among those stopped by the atmosphere, so must be
observed above the Earth\'s atmosphere. The 1960s saw the birth of X-ray
astronomy, with rockets, called \"sounding rockets\", to put instruments
above the bulk of the atmosphere. A \"sounding rocket\" is one that is
used to perform research, and is named after the nautical term *to
sound*, meaning, \"to take a measurement\". A sounding rocket has a
typical science observing time of 5-40 minutes (in other words, the
rocket remains above the bulk of the atmosphere for between 5 and 40
minutes, depending on the rocket and how high it flies).

When astronomers first thought about X-rays from astronomical sources,
the general opinion was that extra-solar sources would be too faint to
be detectable. The first X-ray detector flown on a sounding rocket was
set to look at the moon, under the idea that heavy particles from the
sun would cause X-ray fluorescence of the moon\'s surface. They did not
detect the moon. Luckily, it just so happened that an X-ray source was
near enough to the moon that the detector could \"see\" it. This source
is now called Scorpius X-1, because it was the first X-ray source
observed in the direction of the constellation Scorpius. It was clear
that Scorpius X-1 came from outside our solar system -- disproving the
idea that extra-solar sources would be too faint to see!

This article discusses two specific X-ray sources in the sky, Taurus
XR-1 and Ophiuchus XR-1. Early X-ray observations were named after the
constellation in which they were found, and numbered in the order that
they were discovered. So Taurus XR-1 was the first X-ray source found in
the constellation Taurus. Similarly, Ophiuchus XR-1 was the first X-ray
source observed in the constellation Ophiuchus.

As previously mentioned, astronomers originally thought that cosmic
X-ray sources would be too weak to be observed, so the appearance of
numerous X-ray sources was a bit of a mystery. This article reports one
of the first attempts to unravel the mystery, pointing out the
similarity between the distributions of supernovae remnants in our
Galaxy and that of the observed X-ray sources. This view was bolstered
by the possibility of two X-ray sources coinciding with known supernova
remnants.

  -----------------------------------------------------------------------
  ![](media/image19.jpeg){width="3.4722222222222223in"
  height="3.4722222222222223in"}

  X-ray image of the Crab nebula as observed by Chandra. The details seen
  in this image are only possible with modern instrumentation -- the
  original observations of the Crab would have been in the form of a
  spectrum, rather than an image. More information on this image
  available here: http://chandra.harvard.edu/photo/2002/0052/\
  *Image credit: NASA/CXC/ASU/J. Hester et al.*
  -----------------------------------------------------------------------

Taurus XR-1 was conclusively tied to the Crab nebula -- a remnant of the
supernova of 1054. The Crab nebula is currently one of the most-studied
objects in the sky, exhibiting emission at all wavelengths from radio to
gamma-ray. It is unclear, however, if Ophiuchus XR-1 turned out to be
from the remnant of SN 1604, also known as Kepler\'s Supernova.
Ophiuchus XR-1 was only conclusively observed by one rocket observation.
However, later observations did find X-ray emission from SN 1604. It is
possible that the first observation was merely noise.

We now know that supernova remnants can leave behind X-ray sources
(neutron stars or black holes); however, supernova remnants are hardly
the only source of cosmic X-rays. X-ray astronomy has grown since the
1960s, with several dedicated satellites, including the well-known
Chandra observatory.

#### Other resources

The following web pages have more detailed information:

-   [What is a Sounding
    Rocket?](http://www.nasa.gov/missions/research/f_sounding.html):
    http://www.nasa.gov/missions/research/f_sounding.html

-   [A Brief History of High Energy
    Astronomy](http://heasarc.gsfc.nasa.gov/docs/heasarc/headates/heahistory.html):
    http://heasarc.gsfc.nasa.gov/docs/heasarc/headates/heahistory.html

-   [Constellation
    Ophiuchus](http://seds.org/Maps/Stars_en/Fig/ophiuchus.html):
    http://seds.org/Maps/Stars_en/Fig/ophiuchus.html

-   [Constellation
    Taurus](http://seds.org/Maps/Stars_en/Fig/taurus.html):
    http://seds.org/Maps/Stars_en/Fig/taurus.html

-   [Supernova 1054 - Creation of the Crab
    Nebula](http://seds.org/messier/more/m001_sn.html):
    http://seds.org/messier/more/m001_sn.html

-   [SN 1604, Kepler\'s
    Supernova](http://seds.org/~spider/Spider/Vars/sn1604.html):
    http://seds.org/\~spider/Spider/Vars/sn1604.html

-   [Chandra website](http://chandra.harvard.edu/):
    http://chandra.harvard.edu/

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Quasars: Express Trains to the Netherworld

*The primary message of this article is the idea that there are objects
near the edge of the known Universe that appear to be speeding away from
us due to the expansion of the Universe. Secondary messages include the
use of Hubble\'s law to determine distances and the shear power of some
of the objects in the Universe that we are able to see them given the
huge distances involved.*

Quasars were first observed with radio telescopes in the 1950s -- they
were seen in radio wavelengths with no corresponding visible object.
When the first quasar was tied to an optical source (a source called 3C
48), its visible spectrum showed odd emission lines. Remember that
different elements have signature emission lines, so it was unusual to
see an object with unidentified lines.

In 1962, a second object, called 3C 273, was connected to an optical
source. Astronomers subsequently made a detailed optical spectrum which
showed unusual emission lines, similar to 3C 48. The unusual lines
turned out to be hydrogen lines redshifted more than any other object
had shown. The reason the lines looked unusual was not because they had
not been seen before, but because they had not been seen in the observed
waveband before.

One of the most important concepts in this article is how the \"speed\"
of an object, or its redshift, is related to the distance of that
object. In the 1929 edition of the Cosmic Times, we introduced this idea
with Hubble\'s Law relating the redshift of an object to its distance.
Quasars are an example of how this redshift-distance relationship was
used in astronomy to determine the nature of an object. Using the large
redshifts measured from the \"unusual\" spectra, astronomers determined
that quasars lie at the edge of the known universe. The size of the
Universe listed in the 1965 Cosmic Times is based on quasar distances.

After 1965, astronomers have identified quasars as a class of active
galactic nuclei. A galaxy with an active nucleus is one that exhibits a
high amount of emission from its nucleus, often so high that it
outshines the galaxy itself. An active galactic nucleus is powered by a
supermassive black hole (a black hole with the mass of a million, or
more, suns). The black hole itself does not radiate, since once a black
hole has swallowed something, even light, it can never return. However,
as the black hole pulls in material, it forms a disk and the material
experiences a lot of friction as it travels in that disk toward the
central black hole. Hot matter can radiate a lot of energy.

#### Other resources

The following web pages have more detailed information:

-   [Active Galaxies and
    Quasars](http://imagine.gsfc.nasa.gov/docs/science/know_l1/active_galaxies.html):
    http://imagine.gsfc.nasa.gov/docs/science/know_l1/active_galaxies.html

-   [Gene Smith\'s Astronomy Tutorial Quasars & Active
    Galaxies](http://cass.ucsd.edu/public/tutorial/Quasars.html):
    http://cass.ucsd.edu/public/tutorial/Quasars.html

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Galaxies Still Misbehaving

*One message of this article is that there is mass in this universe that
we cannot account for by studying light alone. In fact, there isn\'t
just a little more matter, but there is **a lot** more mass. A secondary
message is that we can observe phenomena in our universe by their
influences on other parts of the universe -- in this case, we observe
the presence of dark matter through its affect on the motions of
galaxies and galaxy clusters.*

This article is the first that deals with the idea of dark matter in the
Cosmic Times. However, astronomers had discovered evidence of dark
matter, or \"unseen matter\" in the 1930s. The location of dark matter
observed in the 1930s was a bit different than that reported here (a
cluster of galaxies versus a single galaxy), but the reasons for
concluding that something was missing, something that we couldn\'t see,
were similar for each discovery.

#### Observations Leading to the Idea of Dark Matter

Fritz Zwicky published the earlier discovery in 1933. Zwicky had
observed the Coma cluster of galaxies, and seen that the speed of the
galaxies in the cluster was too great for the amount of mass he could
account for. By his calculation, the galaxies in the cluster should have
been flung free of the cluster.

This story in the 1965 Cosmic Times reports that astronomers have found
two galaxies that are rotating faster than they should be able to based
on the mass calculated from the luminous matter (or matter that shines
on its own, such as stars). In fact, the measurements indicated that if
there was not more mass in these objects than meets-the-eye, the outer
reaches of the galaxy should have been flung free of the galaxy long
ago.

#### How the Presence of Dark Matter is Detected

In both observations of missing mass, astronomers observed that an
object (galaxy or cluster of galaxies) was rotating too fast for the
amount of mass in luminous matter. In the case of a galaxy cluster, the
rotation can be measured approximately by measuring the redshifts
galaxies in the cluster. For the case of a galaxy, astronomers can
measure the rotation of a galaxy by measuring the redshift of different
\"slices\" of the galaxy, as illustrated below.

  -----------------------------------------------------------------------
  ![](media/image20.png){width="5.426388888888889in"
  height="4.208333333333333in"}

  This illustration shows how an astronomer might take redshift
  measurements of different slices of a galaxy to construct a rotation
  curve. (The center of the galaxy does not have a redshift (or
  rotational velocity) of zero because the galaxy has an intrinsic
  redshift due to the expansion of the Universe.)
  -----------------------------------------------------------------------

Using redshifts for many slices of a galaxy, astronomers construct a
\"rotation curve\" for the galaxy, plotting the distance from the center
of the galaxy versus the rotation rate.

Now, if most of the mass is concentrated at the center of the galaxy, as
is observed with the stars of a galaxy, we would expect that the stars
at the outer edges of the galaxy would rotate slower and slower as you
moved out. Instead, the observed rotation curves flatten out at the
outer edges of the galaxy. This observation implies that the amount of
matter in the galaxy does not taper out in the same manner that the
luminous matter tapers out. In other words, there must be a lot of
matter in the galaxy that is not seen as luminous matter.

It was not unexpected that some matter would be unseen in galaxies.
Certainly, astronomers knew that stars died, and stopped shining,
leaving behind non-luminous corpses. However, it was expected that
luminous matter would be a tracer of all matter in a galaxy -- in other
words, the corpses of stars, which might account for much of the unseen
matter, should lie in regions where stars have formed and are still
shining. Instead, they found that there was much more mass than could be
accounted for by the observed luminosity from the galaxy, and the
distribution of that mass did not follow the distribution of light in
the galaxy.

In 1965, dark matter is a growing mystery in astronomy. We will revisit
dark matter in both the 1993 and 2006 editions of Cosmic Times. In fact,
scientists continue to puzzle about the nature of dark matter, even
today.

#### Other resources

The following webpages have more detailed information:

-   [RotCurve](http://burro.astr.cwru.edu/JavaLab/RotcurveWeb/main.html)
    -- a site with a Java applet that allows you to play with the
    different components of a galaxy to see that there is no way to fit
    the observed rotation curves with luminous matter as the tracer of
    matter in the galaxy:
    http://burro.astr.cwru.edu/JavaLab/RotcurveWeb/main.html

# 1993 Cosmic Times

This edition, the fifth of the series, features the discovery of
anisotropies in the cosmic microwave background (CMB). These tiny
variations in the remnant radiation from very early in the Universe
eventually formed the structures that we see around us today. By the
early 1990s, astronomers have extended the Big Bang theory to include a
period of inflation to make the theory better align with observations.
The distance scale has been refined based on a class of supernova,
allowing distance determinations to ever-further galaxies. In addition,
the Nobel Prize for physics awarded to a pair of scientists who
discovered proof of gravitational waves.

The language in the 1993 newspaper mimics the style of writing that
would have appeared in a newspaper at that time. The style is similar to
modern-day newspapers, and should be easier to read than previous
editions; though, the concepts continue to get harder. The poster also
shows a layout that mimics the papers of the time (note the introduction
of color); however, we have taken some creative license to make it more
readable in a classroom setting.

![](media/image21.jpeg){width="3.5in" height="4.813194444444444in"}

**Summary of the 1993 Articles**

### 

### Baby Universe's 1^st^ Picture

In the early 1990s, the COBE satellite confirmed the spectrum of the
cosmic microwave background to be a perfect black body, as predicted by
astronomers. It also made the first complete map of the tiny
fluctuations in the temperature of the background. This discovery was a
watershed event. Astronomers had known that this remnant radiation from
the Big Bang could not be infinitely smooth. This is because we have a
"lumpy" universe now, with clumps of matter that form structures we see
today. The discovery of the anisotropy confirmed astronomer's ideas
about the Big Bang.

### Pancake or Oatmeal Universe -- What's for Breakfast?

Despite the fluctuations discussed in the "Baby Universe" article, the
microwave background is remarkably smooth. This brief sidebar discusses
the differences between the apparent smoothness of the distribution of
matter in the early universe to lumps of matter (in the form of
galaxies) we see today. It sets up the "Inflation in the Universe"
article.

### Inflation in the Universe

This article explains how inflation theory addressed a problem faced by
the Big Bang -- the universe is too big for the cosmic microwave
background to be as smooth and uniform as it is. To solve this,
astronomers introduced a very short period of very rapid expansion just
after the Big Bang. An underlying message of this article is that
theories, such as the Big Bang, often undergo revision and changes.

### Dark Matter Hunt Heats Up

In the 1990s, the evidence for dark matter expanded to include
observations of hot X-ray gas in a group of galaxies. The observations
showed that the visible mass of the galaxies was insufficient to hold
such energetic gas in place. Hence, dark matter must be present. While
previous *Cosmic Times* editions have touched on dark matter, we find
that exploring in wavelengths other than visible light provides
compelling new evidence.

### Fool-Proofing Galactic 'Candles'

This article continues the story of how astronomers refine their
"standard candles" to determine distances to far away galaxies. This
article picks up the story of supernovae and different types of
supernovae discussed in the 1955 edition of *Cosmic Times*. In the early
1990s, astronomers refined their understanding of Type Ia supernovae so
that they could be more reliably used as standard candles. Type 1a
supernovae can be observed in objects at much further distances that the
other standard candle, Cepheid variables, discussed in earlier editions
of *Cosmic Times*. This development sets up a key tool that will play an
important role in the 2006 edition of *Cosmic Times*.

### Pulsar Gravitational Waves Win Nobel Prize

In 1993, the Nobel Prize for physics was awarded to Russell Hulse and
Joseph Taylor of Princeton University. The prize was awarded for their
discovery of the first pulsar in a binary system and subsequent work
using the arrival times of pulses from the pulsar to give the first
evidence of gravitational waves. This article illustrates that
scientists continually test their theories, and that after nearly 80
years Einstein's theory of relativity continues to pass those tests.

## Notes on 1993 Articles

### 

### Baby Universe\'s 1^st^ Picture

*The primary message of this article is that the discovery of tiny
variations in the cosmic microwave background was a watershed event.
Astronomers had known that this remnant radiation from the Big Bang
could not be infinitely smooth. This is because we have a \"lumpy\"
universe now, with clumps of matter that form structures we see today.
The discovery of the anisotropy confirmed astronomer\'s ideas about the
Big Bang.*

#### Helping your students understand the concepts

The ideas presented in this article may be easier for your students to
understand if they have first read and discussed the 1965 Cosmic Times
article on the cosmic microwave background, *Murmur of a Bang*. The 1965
Cosmic Times lesson plan titled \" Cosmic Microwave Background\" may
also help your students develop a solid understanding of the CMB.

In addition, we suggest that the lesson plan titled \"What\'s the
Problem with Isotropy\" used after reading this article may help
students understand the main concepts presented in this article.

#### The COBE satellite

The 1965 Cosmic Times introduced the observation by Penzias and Wilson
of a radiation background left over from a time just after the Big Bang
bathing the entire Universe. As with any astronomical discovery, the
first observations serve to prove that a phenomenon exists. Astronomers
scramble after such a discovery to develop methods and technologies to
study the phenomenon in greater detail. The cosmic microwave background
(CMB) is no different. NASA solicited for proposals for small- or
medium-sized space missions in the early 1970s, and received three
independent proposals to study the CMB. This sent NASA the message that
the astronomical community wanted to study the CMB in greater detail,
and that they had many ideas about how to carry out those studies. NASA
responded by selecting members from each of the three teams to join
together for a unified mission. The end result was Cosmic Background
Explorer (COBE), which launched in 1989.

The three instruments COBE carried were designed for two primary tasks:
measuring the CMB spectrum and mapping the CMB. One instrument made a
detailed spectrum of the CMB. The other two instruments mapped the CMB
across the entire sky.

#### The COBE spectrum

Using just the first 9 minutes of data from the spectrometer, COBE
scientists were able to make a spectrum of the CMB. Shown below.

  -----------------------------------------------------------------------
  ![](media/image22.jpeg){width="5.1625in" height="3.8805555555555555in"}

  This is the spectrum that John Mather presented at the January 1990
  meeting of the American Astronomical Society Meeting. It is the
  spectrum based on the first 9 minutes of data from COBE. The solid line
  shows a theoretical blackbody, and the squares show the COBE data. The
  error bars for the data are contained within the squares.
  -----------------------------------------------------------------------

One thing to notice about the plot is that the theoretical blackbody
(solid line) and the data (squares) match *precisely*. Astronomers
rarely see data and theory matching so precisely. In fact, when John
Mather presented this very plot at the 1990 meeting of the American
Astronomical Society Meeting, it was greeted with a standing ovation.

This spectrum was the first result from COBE, and it was enough to make
some astronomers a little nervous. Why is that? Because the data is
*too* smooth. Let\'s take a quick inventory of the Universe around us.
There are planets, stars, galaxies and cluster of galaxies. In a word,
it\'s clumpy. In other words, the matter is generally found in
gravitationally bound structures.

The structure we see today must have come from seeds in the early
Universe. But the CMB is a reflection of that early Universe, so those
seeds must be present in the CMB or we would not see structure today.
The smooth spectrum contained no hints of those seeds. The astronomical
community would have to wait another 2 years to see if the maps made by
COBE\'s other instruments contained the seeds that needed to be there to
produce our present-day Universe.

#### The COBE Map

In 1992, George Smoot\'s team published COBE\'s map of the CMB, and for
the first time astronomers saw the \"lumps\" in the CMB. These
anisotropies, as astronomers call them, were at the very limit of
COBE\'s capabilities, but were large enough to eventually form the
structure that we see in the Universe today. The map is shown below:

  -----------------------------------------------------------------------
  ![](media/image23.png){width="5.660416666666666in"
  height="2.829861111111111in"}

  COBE cosmic microwave background radiation (CMB) map.
  -----------------------------------------------------------------------

The different colors show places where the very early Universe had
temperature differences, which are equivalent to density differences.
Higher density regions were the places where gravity started to form
structures. We know that these anisotropies must be the seeds of
structure that we see today, but the details of COBE are too coarse to
identify specific seeds with present-day structures.

One important point is that while we talk about \"lumps\" in the early
Universe, the size of those density differences was tiny. They represent
changes of the order of 1 part in 100,000. Changes of this size are a
bit like locating a single mosquito on a stretch of road a mile long.
That\'s a small difference in density! In fact, the background was so
smooth that other problems with Big Bang Theory arose even before these
COBE results. However, these other problems are solved with inflation,
as is discussed in the article titled \"Inflation in the Universe\".

Perhaps the most important point for students to walk away with is that
on the one hand, we have very, very small changes in the background, but
those changes turn out to be essential to the Universe we observe today.
Big Bang theory would have been in a heap of trouble if astronomers
hadn\'t seen those tiny changes in the CMB.

#### Other resources

The following web pages have more detailed information:

-   [COBE website](http://lambda.gsfc.nasa.gov/product/cobe/):
    http://lambda.gsfc.nasa.gov/product/cobe/

-   [Discovery Education
    Streaming](http://streaming.discoveryeducation.com/) -- if your
    school has an account with Discovery Education Online, they have
    several videos and clips discussing the cosmic microwave background
    and the expanding universe: http://streaming.discoveryeducation.com/

-   The Beyond the Solar System DVD has a few clips that deal with the
    cosmic microwave background and how the structure we see in the CMB
    were transformed into the Universe we see today. This DVD can be
    requested from the following [web
    page](http://cfa-www.harvard.edu/seuforum/btss/dvd/):
    http://cfa-www.harvard.edu/seuforum/btss/dvd/

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Sidebar: Pancake or Oatmeal Universe -- What\'s for Breakfast?

*The primary message of this article is to further differentiate the
definitions of \"smooth\" and \"lumpy\" as they pertain to the cosmic
microwave background.*

The articles about the comic microwave background (CMB) in this edition
of Cosmic Times talk about it being lumpy and being smooth, so this
sidebar aims to clarify the different definitions as they apply to
cosmology.

The first thing to remember is that when astronomers talk about
structure in the CMB, they are really talking about structure in the
Universe shortly after the Big Bang. By most definitions, the CMB is
quite uniform (or smooth). In fact, the level of uniformity caused some
problems for cosmologists, which we discuss in the article on Inflation
Theory, \"Inflation in the Universe\". The anisotropies, or \"lumps\",
that astronomers found in the CMB were tiny. The magnitude of the
anisotropies was just 1 part in 100,000, which in length scales would be
is like the width of a human hair compared to a full-sized school bus.

Most of the matter that we see in the Universe around us now is in the
form of \"clumps\": planets, stars, nebula, star clusters, galaxies, and
clusters of galaxies. This is a huge difference from the early Universe
as seen in the CMB. It is important for students to understand these
distinctions.

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Inflation in the Universe

*The primary message of this article is to show that Big Bang theory has
gone through changes since it was first conceived. Observations of the
cosmic microwave background posed problems for the theory as it stood,
so theorists developed Inflation Theory to better account for those new
observations.*

#### The Problem

In the article titled \"Universe\'s 1^st^ Baby Picture\", we found that
the cosmic microwave background was very, very smooth. There were
density differences, but as we discuss in the article and the article
notes, those differences are *very* small. In fact, the CMB was so
uniform that it posed a problem for Big Bang theory. In cosmology, this
is called the Horizon Problem. \*

It is not unusual for a scientific theory to undergo revisions when new
observations conflict with its predictions. In fact, this is the very
heart of the scientific process. Students may be surprised that, more
often than not, theories generally undergo revision rather than being
discarded wholesale when new observations do not support the theory.
Theorists work to incorporate the new observations into the theory with
as little change as possible to the original theory, because the theory
presumably worked pretty well for observations prior to the new
observations.

Big Bang theory is no different from any other scientific theory, and
even before the COBE results, it was becoming clear that the background
was too uniform. The reason this was a problem was that regions of the
CMB that should not have had time to \"talk\" to each other were
essentially in thermodynamic equilibrium. This was a problem.

To better understand this problem, consider a mug of hot coffee. If we
drop an ice cube into it, we know that eventually the ice cube will melt
and warm up while the hot coffee will cool down a little, and liquid in
the mug will come to the same temperature throughout. Once the liquid is
all at the same temperature again, scientists would say that the liquid
is in \"thermodynamic equilibrium\".

For this illustration, let\'s say that it takes 15 minutes for the
liquid to come back to thermodynamic equilibrium. Up until that
15-minute mark, different areas inside the coffee mug will have
different temperatures. Early on, the differences are especially
pronounced. During the first minute, the coffee will be relatively cool
near the ice cube, but the coffee toward the bottom of the mug will
still be close to its original temperature. The way astronomers might
describe this is that different parts of liquid in the mug have not had
time to \"communicate\" with each other.

+--------------------+-------------------------------------------------+
| **Thermodynamic    |                                                 |
| Equilibrium in a   |                                                 |
| Coffee Mug**       |                                                 |
+--------------------+-------------------------------------------------+
| Add an ice cube to | ![](media/image24.png){width="3.81875in"        |
| a mug of hot       | height="6.297916666666667in"}                   |
| coffee.            |                                                 |
|                    |                                                 |
| Just after the ice |                                                 |
| is placed in the   |                                                 |
| mug, the coffee at |                                                 |
| the bottom of the  |                                                 |
| mug will be close  |                                                 |
| to its original    |                                                 |
| temperature, while |                                                 |
| coffee immediately |                                                 |
| surrounding the    |                                                 |
| ice cube will be   |                                                 |
| cooler.            |                                                 |
|                    |                                                 |
| Right as the ice   |                                                 |
| cube disappears,   |                                                 |
| let\'s say at      |                                                 |
| minute 5, there    |                                                 |
| will be a          |                                                 |
| temperature        |                                                 |
| difference between |                                                 |
| coffee in          |                                                 |
| different parts of |                                                 |
| the mug.           |                                                 |
|                    |                                                 |
| Eventually, all of |                                                 |
| the coffee in the  |                                                 |
| mug will be at the |                                                 |
| same temperature.  |                                                 |
| This final         |                                                 |
| temperature will   |                                                 |
| be slightly lower  |                                                 |
| than the original  |                                                 |
| temperature of the |                                                 |
| coffee. However,   |                                                 |
| the final          |                                                 |
| temperature will   |                                                 |
| be significantly   |                                                 |
| higher than the    |                                                 |
| original           |                                                 |
| temperature of the |                                                 |
| ice, because there |                                                 |
| is so much more    |                                                 |
| coffee than ice.   |                                                 |
+--------------------+-------------------------------------------------+

Taking the coffee mug analogy one step further, let\'s imagine that we
measure the temperature at all parts of the mug 10 minutes after adding
the ice cube. We know that the liquid in the mug should be at different
temperatures depending on where we measure, so if our measurement showed
a uniform temperature everywhere in the coffee mug, we would be very
surprised. The Big Bang model, as it existed before Inflationary Theory,
predicted that the Universe should not have been in thermodynamic
equilibrium when the CMB was emitted. In other words, the Universe would
be so large that parts of the Universe should not have been able to
communicate before the CMB was created. So we had every reason to
believe that the CMB measured in opposite directions should have shown
different temperatures. The observations, however, found that the
temperature was uniform in every direction.

+-----------------------------------+----------------------------------+
| **The Universe without            |                                  |
| Inflation:\                       |                                  |
| Prediction versus observation**   |                                  |
+-----------------------------------+----------------------------------+
| **What we expected**              | **What we measured**             |
|                                   |                                  |
| Below is a cut-away of the coffee | Below is a cut-away of the       |
| mug with colors indicating the    | coffee mug with colors           |
| temperature gradient that we      | indicating the temperature       |
| might expect to measure 10        | gradient that we measured at 10  |
| minutes after we add the ice      | minutes after adding the ice     |
| cube. The liquid in the mug has   | cube. The consistent temperature |
| not had time to reach             | was not expected because coffee  |
| thermodynamic equilibrium, so     | should not have had time to come |
| there is a temperature gradient,  | to thermodynamic equilibrium.    |
| with blue indicating cooler       |                                  |
| temperatures and red indicating   | This is analogous to the         |
| hotter temperatures.              | measurements of the CMB prior to |
|                                   | Inflation Theory -- cosmologists |
| Toward the top of the mug, the    | needed to explain why the        |
| coffee is cooler because of the   | temperature was so consistent    |
| melted ice cube. Toward the       | when the Universe should not     |
| bottom of the mug, the coffee is  | have had time to come to         |
| hotter because it has not had     | thermodynamic equilibrium before |
| time to mix with the cooler       | the CMB was emitted.             |
| liquid at the top of the mug.     |                                  |
+-----------------------------------+----------------------------------+
| ![](media/image25.                | ![](media/image26.j              |
| jpeg){width="2.361111111111111in" | peg){width="2.361111111111111in" |
| height="2.1805555555555554in"}    | height="2.1805555555555554in"}   |
+-----------------------------------+----------------------------------+

#### 

#### The Solution: Inflation

Inflation Theory answers the Horizon Problem by proposing that early in
the Universe\'s history, a small parcel of space expanded rapidly. This
expansion increased the size of the Universe by a factor of 10^26^ in a
fraction of a second. This might sound like it violates relativity,
because the expansion occurs faster than the speed of light. However,
the expansion is of *space* only, with no matter or information carried
between points at faster than the speed of light.

The Horizon Problem is solved with inflation because prior to the
episode of inflation, those regions that are on different sides of the
Universe today were actually much, much closer than they would have been
without Inflation. That means that parts of the CMB that look very
distant today actually would have had time to \"communicate\" early in
the Universe\'s history because they were much closer then and in
thermodynamic equilibrium. This explains why their temperatures are so
similar now.

Returning to the coffee mug analogy, this time we will take a much
smaller mug of coffee and add an ice cube. Because there is less liquid
that needs to come to thermodynamic equilibrium, it will happen much
faster. Imagine that thermodynamic equilibrium occurs 5 minutes after
adding the ice cube. At 7 minutes after adding the ice cube, increase
the size of the mug by a factor of 4, and measure the temperature
everywhere in the mug a few minutes later. We wouldn\'t be surprised if
the temperature was uniform throughout the coffee in the mug, because it
was in thermodynamic equilibrium before the expansion. This is what
happened in the universe, except the universe expanded by a factor of
10^26^!

+-----------------------+----------------------------------------------+
| **The Universe with   |                                              |
| Inflation**           |                                              |
+-----------------------+----------------------------------------------+
| Add an ice cube to a  | ![](me                                       |
| small mug of hot      | dia/image27.png){width="3.964583333333333in" |
| coffee.               | height="6.602777777777778in"}                |
|                       |                                              |
| Just after the ice is |                                              |
| placed in the mug,    |                                              |
| the coffee at the     |                                              |
| bottom of the mug     |                                              |
| will be close to its  |                                              |
| original temperature, |                                              |
| while coffee very     |                                              |
| close to the ice cube |                                              |
| will be at a lower    |                                              |
| temperature.          |                                              |
|                       |                                              |
| However, with a       |                                              |
| smaller mug, the      |                                              |
| coffee and ice cube   |                                              |
| will come to          |                                              |
| thermodynamic         |                                              |
| equilibrium much      |                                              |
| faster; let\'s say 5  |                                              |
| minutes after         |                                              |
| dropping the ice cube |                                              |
| into the mug. Now,    |                                              |
| all parts of the      |                                              |
| coffee are the same   |                                              |
| temperature.          |                                              |
|                       |                                              |
| In Inflationary       |                                              |
| Theory, after the     |                                              |
| early universe came   |                                              |
| to thermodynamic      |                                              |
| equilibrium, but      |                                              |
| before the cosmic     |                                              |
| microwave background  |                                              |
| was emitted, the      |                                              |
| universe underwent a  |                                              |
| rapid expansion. So,  |                                              |
| in our coffee-mug     |                                              |
| model, our small mug  |                                              |
| of coffee expands     |                                              |
| sometime after it     |                                              |
| comes to              |                                              |
| thermodynamic         |                                              |
| equilibrium.          |                                              |
|                       |                                              |
| Note: The             |                                              |
| illustration scale    |                                              |
| and timing are not to |                                              |
| scale with the        |                                              |
| Universe\'s period of |                                              |
| inflation.            |                                              |
+-----------------------+----------------------------------------------+

\*Big Bang Theory had three different problems that are accounted for in
Inflation Theory: The Flatness Problem, The Horizon Problem, and The
Monopole Problem. We concentrate on the Horizon Problem here because it
is the easiest to understand. For more information on the other problems
and how they are solved with Inflation Theory, follow the links under
\"Other Resources\" below.

#### Other resources

The following web pages have more detailed information:

-   [What is Inflation
    Theory?](http://map.gsfc.nasa.gov/universe/bb_cosmo_infl.html):
    http://map.gsfc.nasa.gov/universe/bb_cosmo_infl.html

-   [Inflation for Beginners by John
    Gribbon](http://www.lifesci.sussex.ac.uk/home/John_Gribbin/cosmo.htm):
    http://www.lifesci.sussex.ac.uk/home/John_Gribbin/cosmo.htm

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Dark Matter Hunt Heats Up

The primary message of this article is that evidence for dark matter has
been found in the X-ray observations of a galaxy cluster. While previous
Cosmic Times editions have touched on dark matter, this time we are
finding evidence in a new wavelength.

Dark matter is one of the hot topics of the late 20^th^ century (and
today). In the Cosmic Times, we first encountered dark matter in the
1965 edition, with the rotation curves of galaxies. However, as we
discussed in the notes to *Galaxies Still Misbehaving*, earlier evidence
for dark matter came from Fritz Zwicky when he observed clusters of
galaxies. Zwicky observed that galaxies in the cluster were moving too
fast to be gravitationally bound to the visible mass in the cluster.
X-ray observations have uncovered further evidence for unseen mass in
clusters of galaxies.

The particular discovery discussed is this article is from the ROSAT
satellite, an X-ray observing satellite that launched in 1990. ROSAT
observed a group of galaxies and found a cloud of hot gas lying between
the galaxies. Out in open space a cloud of hot gas would typically
dissipate rather quickly. In order to keep a cloud of hot gas together
for any length of time, the gas must be gravitationally bound to the
galaxies in the group. However, the mass of the galaxies and gas were
not enough to bind the hot gas to the group of galaxies. This
observation led to the conclusion that there must be more mass in the
group of galaxies than could be seen -- further evidence for dark
matter.

A back-of-the-envelope calculation can be done for the ROSAT data by
comparing the kinetic energy of the hot gas to the gravitational energy
of the mass of the galaxies plus gas. One of our lesson plans, "Dark
Matter NASA Conference", goes through the calculations using the real
measurements from ROSAT.

#### Other resources

The following web pages have more detailed information:

-   [ROSAT data hint at a closed
    Universe](http://findarticles.com/p/articles/mi_m1200/is_n2_v143/ai_13324072):
    http://findarticles.com/p/articles/mi_m1200/is_n2_v143/ai_13324072

-   [ROSAT mission web
    page](http://heasarc.gsfc.nasa.gov/docs/rosat/rosgof.html):
    http://heasarc.gsfc.nasa.gov/docs/rosat/rosgof.html

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Pulsar Gravitational Waves Win Nobel Prize

*The primary message of this article is that Einstein\'s theory of
relativity continues to be tested, and it continues to pass those
tests.*

In 1993, the Nobel Prize for physics was awarded to Russell Hulse and
Joseph Taylor of Princeton University. The prize was awarded for their
discovery of the first pulsar in a binary system and subsequent work
using the arrival times of pulses from the pulsar to give the first
evidence of gravitational waves.

#### Pulsars

We can\'t introduce pulsars without first introducing neutron stars. A
neutron star is one of the possible endpoints of stellar evolution. When
a massive star dies in a supernova, the core that it leaves behind can
either collapse into a black hole or into a neutron star (see links
under \"Other Resources\" on stellar evolution for more information on
how neutron stars form). Neutron stars are very dense -- they have about
1.4 times the mass of our Sun smooshed into a volume with a diameter of
about 20 km. Pulsars are neutron stars with strong magnetic fields, from
which we observe pulses of radiation as the neutron star rotates (as
illustrated below).

  -----------------------------------------------------------------------
  ![](media/image28.png){width="3.501388888888889in" height="2.675in"}

  A diagram of a pulsar, showing its rotation axis and its magnetic axis
  -----------------------------------------------------------------------

#### Hulse and Taylor\'s Discovery

Hulse and Taylor first observed the pulsar PSR 1913+16 in 1974 while
they were searching for pulsars. They soon discovered that it was in a
binary system with another star. In fact, PSR 1913+16 was the *first*
pulsar to be found in a binary system. Hulse and Taylor knew that such a
system would be very interesting, particularly in what it could tell us
about relativity in an environment that we can\'t reproduce on or near
the Earth.

PSR 1913+16 and its companion star orbit with a period of 7.75 hours.
PSR 1913+16 rotates with a period of 59 milliseconds, as derived from
the time between its pulses. Hulse and Taylor measured the arrival times
of the pulses of light from PSR 1913+16 as they arrived at Earth. Using
these arrival times, Hulse and Taylor could determine the orbital
properties of the binary system. As the pulsar orbits its companion
star, the pulsar is closer to Earth and the pulses arrive slightly
sooner. When the pulsar is at periastron (the place in the orbit where
the two stars are closest together), the pulses appear bunched together
because the pulsar is moving fastest in its orbit at that point. By
analyzing these pulses and the pulse patterns throughout the orbit of
the pulsar, they were able to find the velocity of the pulsar in its
orbit and subsequently calculate the orbit properties. They found the
orbit is elliptical with a semi-major axis of 500,000 km.

Hulse and Taylor observed the orbit of PSR 1913+16 over time, and found
the signatures of three different relativistic effects in the data.
First, they found a signature of time dilation, such that when the stars
neared each other in their orbit, the gravitational field is stronger,
and the pulses slowed down. Second, they found evidence of the warping
of spacetime, with the periastron of the orbit advancing by 4.2° each
year (much faster than the advance of the perihelion of Mercury\'s
orbit). Third, they found that the orbit itself was shrinking, based on
their observation that the orbital period of PSR 1913+16 and its
companion was decreasing over time. From this they determined that the
size of the orbit was shrinking by 3.1 mm each orbit.

It\'s that shrinking orbit that was evidence for gravitational waves. In
order for the orbit to shrink, energy had to be leaving the binary
system. Einstein\'s General Theory of Relativity predicted that
gravitational waves could carry energy from a system, but no one had
seen evidence for gravitational waves prior to Hulse and Taylor\'s
results. This was the first physical evidence of the existence of
gravitational waves.

Note: The literature often refers to PSR 1913+16 as a \"binary pulsar\".
Be aware that this does not necessarily mean that the two stars in the
system are pulsars. Instead, it simply means that PSR 1913+16 is a
pulsar that lies in a binary system. The term \"binary pulsar\" is not
meant to reveal information about the companion star. In this case it is
likely that the companion is a neutron star, but we do not detect pulses
from it.

#### LISA and the future of gravitational waves

Even today gravitational waves have not been directly observed.
Scientists have been working on the problem since this first discovery,
but gravitational waves are exceedingly hard to detect. Essentially, a
gravitational wave stretches and shrinks spacetime by a tiny amount. So
far, there is one gravitational wave experiment that has conducted
several experimental runs since 2002, but they have not yet seen the
signature of gravitational waves. The next step in detecting
gravitational waves is a space-based mission called LISA (Laser
Interferometer Space Antenna).

Gravitational wave research is currently the very cutting-edge of
astronomy and physics, and is one of the unsolved problems facing
scientists today. With the projected launch of LISA in 2015, current
middle- and high-school students may be the scientists and graduate
students who will see the first direct evidence of gravitational waves.

#### Other resources

The following web pages have more detailed information:

-   [Press release announcing Nobel prize for Hulse and
    Taylor](http://nobelprize.org/nobel_prizes/physics/laureates/1993/press.html):
    http://nobelprize.org/nobel_prizes/physics/laureates/1993/press.html

-   [Taylor\'s Nobel
    Lecture](http://nobelprize.org/nobel_prizes/physics/laureates/1993/taylor-lecture.html):
    http://nobelprize.org/nobel_prizes/physics/laureates/1993/taylor-lecture.html

-   [Hulse\'s Nobel
    Lecture](http://nobelprize.org/nobel_prizes/physics/laureates/1993/hulse-lecture.html):
    http://nobelprize.org/nobel_prizes/physics/laureates/1993/hulse-lecture.html

-   [Neutron Stars and
    Pulsars](http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html):
    http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html

-   [Gravitational
    Waves](http://imagine.gsfc.nasa.gov/docs/features/topics/gwaves/gwaves.html):
    http://imagine.gsfc.nasa.gov/docs/features/topics/gwaves/gwaves.html

-   [LIGO website for all
    audiences](http://www.ligo-la.caltech.edu/index.htm):
    http://www.ligo-la.caltech.edu/index.htm

-   [LISA Mission homepage](http://lisa.nasa.gov/):
    http://lisa.nasa.gov/

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Fool-Proofing Galactic \'Candles\'

*The primary message of this article is that astronomers can use a
certain type of supernova, Type 1a supernova, as a standard candle to
determine distances in the Universe. Type 1a supernovae can be observed
in objects at much further distances that the other standard candle,
Cepheid variables, discussed in earlier editions of Cosmic Times.*

In this article, the Cosmic Times threads of distances in the Universe
and supernovae come together as we discover that one type of supernovae,
Type 1a supernovae, can be used as standard candles. The idea of
standard candles comes up in nearly every edition of the Cosmic Times
because the importance of standard candles in astronomy cannot be
overemphasized -- they are essential for determining distances to
objects in the Universe.

#### Type 1a Supernovae

The last two editions of Cosmic Times have introduced the idea of
supernova and different types of supernovae explosions. We know that
supernovae are essentially exploding stars; however, there are two
primary types of supernovae -- those from a star at the end of its life
and those from a white dwarf exceeding its critical mass. This latter
type of supernovae, called Type 1a supernovae, is the type that we\'re
interested in here.

A low-mass star (one with less than about 10 times the mass of our Sun)
ends rather quietly when it exhausts its supply of material for nuclear
fusion. Without nuclear fusion to hold the core up against gravity, the
core collapses into a white dwarf. A white dwarf is held up against
gravity by what is called \"electron degeneracy pressure\". There is a
limit, however, to the amount of mass that electron degeneracy pressure
can hold against gravity -- 1.4 solar masses. When a white dwarf exceeds
1.4 solar masses, it will explode in a Type 1a supernova.

In general, a white dwarf all by itself in space will not gain mass very
quickly. However, when a white dwarf is in a binary system, its
companion may donate mass through two different mechanisms. If the white
dwarf\'s companion is a massive star, it might put off a strong stellar
wind (like our Sun\'s solar wind, but much stronger). Some of that
stellar wind will be picked up by the white dwarf. A faster method for
the white dwarf gaining mass is if its companion is a low-mass star that
becomes a red giant star. If the two stars are close enough, the red
giant may become \"too big for its britches\" and lose some of its outer
layers of mass to the white dwarf (see image below).

+-----------------------------------------------------------------------+
| ![](media/image29.jpeg){width="4.166666666666667in"                   |
| height="3.2222222222222223in"}                                        |
+-----------------------------------------------------------------------+
| Artist\'s impression of a binary star system with a white dwarf and a |
| low-mass companion that has become a red giant. The red giant         |
| \"donates\" mass to the white dwarf. If the white dwarf\'s mass       |
| exceeds 1.4 solar masses, it will collapse and explode as a Type 1a   |
| supernova.                                                            |
|                                                                       |
| Image Credit:                                                         |
| [CX                                                                   |
| C/M.Weiss](http://chandra.harvard.edu/photo/2001/v1494aql/index.html) |
+-----------------------------------------------------------------------+

#### Type 1a Supernovae as Standard Candles

No matter what the mechanism that causes a white dwarf to gain mass,
once it exceeds 1.4 solar masses, it will explode in a Type 1a
supernova. Because they all explode at approximately the same mass, the
explosions should be pretty much the same, no matter where they occur in
the Universe. This is why astronomers can use Type 1a supernovae as
standard candles. Type 1a supernovae are quite bright, so they can be
observed at very large distances -- much further distances than Cepheid
variables, opening up more of the Universe for detailed study.

This article discusses a correction to the standard candle scale for
slight differences in Type 1a supernovae. These differences might arise
because the progenitor white dwarfs have different abundances of
materials, or perhaps their surrounding environments are different.
Either way, astronomers have determined a correction that accounts for
the differences and re-calibrates the Type 1a distance scale. This sets
up Type 1a supernovae for their important return in the 2006 Cosmic
Times, where they become critical in the discovery of dark energy.

#### Other resources

The following webpages have more detailed information:

-   [Background on the Life Cycles of
    Stars](http://imagine.gsfc.nasa.gov/docs/teachers/lessons/xray_spectra/background-lifecycles.html):
    http://imagine.gsfc.nasa.gov/docs/teachers/lessons/xray_spectra/background-lifecycles.html

-   [White Dwarf
    Stars](http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html):
    http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html

# 2006 Cosmic Times

This edition is the last of the series, with the publication date chosen
to encompass the discovery of dark energy, a puzzling new component of
our Universe that had been undetected until 1997. Since that first
discovery, astronomers have confirmed its presence and its overwhelming
abundance in our Universe. This edition discusses some of the most
recent pieces of evidence for dark energy and NASA's future plans for
pinning down its elusive nature. In so doing, this edition returns to
the cosmic microwave background (CMB), and shows a more detailed map of
the early Universe as observed by the Wilkinson Microwave Anisotropy
Probe (WMAP). In addition, the Nobel Prize is awarded to the pair of
scientists responsible for the two main science results of COBE, which
we introduced in the 1993 Cosmic Times.

The language in the 2006 newspaper mimics the style of writing of
newspapers of today. Hence, it should be easier to read than previous
editions; though, the concepts continue to get harder. We have taken
some creative license to make the newspaper more readable in a classroom
setting.

![](media/image30.jpeg){width="3.5in" height="4.813194444444444in"}

**Summary of the 2006 Articles**

### Faster Walk on the Dark Side 

Recent observations have confirmed the 1997 discovery that the Universe
is expanding at an increasing rate. The energy from this accelerated
expansion makes up nearly 75% of the energy and matter in the Universe.
This article describes the latest evidence for this "dark energy".

### Seeds of Modern Universe 

NASA's Wilkinson Microwave Anisotropy Probe (WMAP) has picked up where
COBE (featured in the 1993 edition of Cosmic Times) left off by
providing a more detailed baby picture of the Universe, with the seeds
of modern structures finally coming through.

### Biggest Mystery: What is Dark Energy? 

The nature of dark energy is still a puzzle, with several theories in
current contention, including the cosmological constant and
quintessence. This article describes astronomers' attempts to understand
this mysterious energy.

### Sorting Out the Dark Stuff 

This article clarifies the difference between two very different unseen
components of the Universe: "dark energy" (seen as a speeding up of the
expansion of the Universe), and "dark matter" (a type of matter whose
effects we see gravitationally).

### "First Light" Wins Nobel 

The scientists responsible for the first detailed spectrum and map of
the cosmic microwave background are honored with the Nobel prize for
physics.

### Journey to Cosmos' Dark Heart 

NASA plans to study the nature of dark energy in more detail by
collecting data for ever-more-distant supernovae. This article describes
the three satellite missions that are currently being considered.

## Notes on the 2006 Articles

### 

### Faster Walk on the Dark Side

*The primary message of this article is that scientists have recently
discovered a new component to the Universe, called dark energy. Dark
energy is causing the expansion of the Universe to accelerate instead of
decelerate, as would have been expected from the effects of gravity. A
secondary message is that there are several lines of evidence for dark
energy.*

There seems to be a feeling that there are no longer any mysteries left
to discover in the Universe. Up until a decade ago, astronomers and
physicists seemed to think that the only thing left was to iron out all
the details. When the discovery of dark energy came along, the entire
scientific community got excited. This type of revolutionary discovery
is something that scientists dream of working on.

In this article introducing dark energy, we used the Integrated
Sachs-Wolfe effect as the anchor point, but it is not the most important
message of the article. Rather, it is more important for your students
to understand that there is something out there that we hadn\'t
previously observed, nor did current theories predict its presence. The
discovery is so new that astronomers do not yet have a good handle on
what it is, but they can characterize its observable effects on the
large-scale structure of our Universe.

#### The Discovery

In the 1929 edition of Cosmic Times, Edwin Hubble had discovered that
the further a galaxy was from the Earth, the faster it was receding. The
relationship between distance and the velocity of a galaxy (or redshift
of that galaxy) was a remarkably straight line. From this, we saw that
the Universe was expanding. The straight line in the distance-velocity
relationship indicates that the expansion occurs at an approximately
constant rate over the timescales that we can measure.

Another thing to note about Hubble\'s Law is that when we look at
further and further galaxies, we are really looking at slices of the
Universe\'s history. This stems from the fact that light takes time to
travel to us, so we really see objects as they were when the light was
emitted. The light we receive from a galaxy that is 50 million light
years away is showing us that galaxy as it looked 50 million years ago.
In this way, astronomers will often use the ideas of distance and time
in the Universe\'s past interchangeably.

As mentioned above, the data prior to 1997 pointed to a fairly constant
rate of expansion in the Universe. However, astronomers did not expect
that to hold indefinitely because of the expected effects of gravity. Of
all of the fundamental forces in physics, gravity works over the largest
distances, and it tends to pull things together. So, over long
timescales, we would expect the expansion to slow down. Astronomers knew
that at some distance, we should start to measure deviations from
Hubble\'s Law due to this slowing expansion.

A natural question is, what would the Hubble plot look like once we
start seeing deviations due to slowing expansion, as we assumed we
should see. Consider a given redshift, or recession velocity, and recall
that we are looking into the past with these observations. If the
expansion rate has been slowing down, then these galaxies should be
closer than they would have with constant expansion. So, we expect that
the points should start to fall below the line, as illustrated below.

  -----------------------------------------------------------------------
  ![](media/image31.png){width="5.3in" height="5.1402777777777775in"}

  Plot of Hubble\'s Law, with the red region showing where points would
  start to fall if the expansion of the Universe is decelerating from the
  effects of gravity.
  -----------------------------------------------------------------------

Prior to 1998, this was what astronomer expected to find, if they could
just observe galaxies at great enough distances. However, in 1998 two
groups of astronomers measured distances to Type 1a supernovae in
distant galaxies. (Recall that the 1993 Cosmic Times introduced the idea
of using Type 1a supernovae as standard candles -- it may be helpful to
review the teacher\'s notes for that article). The groups also measured
redshifts for the galaxies and added their data to a Hubble plot
(distance versus redshift, or velocity). These new observations finally
showed statistically significant deviations from the straight line
normally seen in Hubble\'s Law. However, the deviation was not in the
direction they had expected! Instead of the points starting to fall
below the line, which would be expected from a slowing expansion due to
gravitation, they found that the points started to fall *above* the
line.

  -----------------------------------------------------------------------
  ![](media/image32.png){width="5.0777777777777775in"
  height="4.011111111111111in"}

  Hubble\'s Law showing the addition of distant Type 1a supernovae. Note
  that they all lie above the projected Hubble\'s Law (black line) from
  previous data.\
  *Credit: Perlmutter et al., 1998, Astrophysical Journal, v. 516*
  -----------------------------------------------------------------------

Scientists are cautious when it comes to revolutionary observations, so
the change in astronomers\' thinking did not change right away. The data
needed to be tested further, and more data was needed before the idea of
an accelerating expansion was fully accepted. However, all subsequent
measurements using different independent methods confirmed that the
expansion of the Universe was speeding up, rather than slowing down.
This discovery changed our understanding of the Universe.

Note that in one of the associated lesson plans, titled "Measuring Dark
Energy", students reproduce the deviation from Hubble\'s Law for
themselves with modern supernova data.

#### Integrated Sacks-Wolfe

One type of test of dark energy involves measurements of the cosmic
microwave background (CMB). Recall that the CMB was created just a few
hundred thousand years after the Big Bang (as discussed in the 1965
Cosmic Times article, *Murmur of a Bang* and the 1993 Cosmic Times
article, *Baby Universe\'s 1^st^ Picture*). Since the effects of dark
energy become apparent only over the largest scales, more precisely over
large timescales, the CMB is an ideal laboratory for dark energy
studies.

As the article mentions, gravity is a property of matter, and often we
depict a \"gravitational well\" around massive objects. Such a depiction
is shown below.

  -----------------------------------------------------------------------
  ![](media/image33.png){width="4.694444444444445in" height="1.875in"}

  Illustration of a typical depiction of a gravity well in spacetime. The
  well represents a place in spacetime where a massive object \"dents\"
  spacetime, causing an attraction between the object and other objects.
  The \"well\" in spacetime also causes the paths of light beams to bend
  near the massive object.
  -----------------------------------------------------------------------

For the largest structures in the Universe (such as a supercluster of
galaxies), dark energy will have a noticeable effect on the energy of a
CMB photon crossing through its gravitational well. The photon gets a
boost in energy when entering the gravitational well. Normally, the
photon would lose that extra energy as it climbs back out of the well.
However, dark energy stretches, and slightly squashes, the gravitational
well over the time it takes the photon to travel across large
structures. It takes less energy for the photon to escape the well than
it received on the way into the well. So the exiting photon keeps a
portion of that extra energy.

  -----------------------------------------------------------------------
  ![](media/image34.png){width="5.998611111111111in"
  height="4.901388888888889in"}

  This illustration shows how the Sachs-Wolfe effect works. As a photon
  from the cosmic microwave background enters the potential well of a
  supercluster of galaxies, it starts with a certain energy. As it
  travels through the supercluster, the photon gains energy until it is
  at the bottom of the potential well. In the absence of dark energy, the
  photon would lose all of its gained energy on its trip out of the
  potential well of the supercluster. However, dark energy will cause the
  supercluster to expand, slightly shrinking the potential well. The
  exiting photon will retain some of the energy it gained on its trip
  through the supercluster.
  -----------------------------------------------------------------------

When astronomers look across the sky, the spectrum of the CMB will be
slightly different in regions where those photons have crossed
gravitational wells that have been shrinking.

#### Other resources

The following web pages have more detailed information:

-   [Integrated Sachs-Wolfe
    Effect](http://ifa.hawaii.edu/cosmowave/supervoids/the-integrated-sachs-wolfe-effect/),
    with a nice animation of the CMB photons gaining energy as they pass
    through a supercluster:
    http://ifa.hawaii.edu/cosmowave/supervoids/the-integrated-sachs-wolfe-effect/

-   [Dark Energy: Astronomers Still \'Clueless\' About Mystery Force
    Pushing Galaxies Apart:
    http://www.space.com/scienceastronomy/astronomy/cosmic_darknrg_020115-1.html](http://www.space.com/scienceastronomy/astronomy/cosmic_darknrg_020115-1.html)

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Seeds of Modern Universe

*The primary message of this article is that a recent NASA mission, the
Wilkinson Microwave Anisotropy Probe (WMAP) has returned a more-detailed
map of the cosmic microwave background (CMB), which is allowing
cosmologists to begin to connect early density differences with
present-day large-scale structures in our Universe.*

#### Wilkinson Microwave Anisotropy Probe (WMAP)

After the success of the COBE mission, as discussed in the 1993 edition
of Cosmic Times, cosmologists wanted to follow-up with a mission that
could map the cosmic microwave background (CMB) in greater detail. The
result was the Wilkinson Microwave Anisotropy Probe (WMAP). The first
WMAP map of the CMB was released in February 2003. A more refined map
released in March 2006, which is the one highlighted in this edition of
Cosmic Times. As of August 2008, WMAP continues to scan the sky,
creating a more-and-more detailed map of the CMB.

The images below show the maps from COBE and WMAP to illustrate the
increased detail in the WMAP data.

  ------------------------------------------------------------------------
  COBE image: ![](media/image35.png){width="5.555555555555555in"
  height="2.7777777777777777in"}\
  WMAP image: ![](media/image36.png){width="5.555555555555555in"
  height="2.7777777777777777in"}

  Two maps of the cosmic microwave background.\
  Top: The map from COBE. (*Credit:
  [COBE/NASA](http://lambda.gsfc.nasa.gov/product/cobe/dmr_image.cfm)*)\
  Bottom: The map from WMAP. (*Credit:
  [WMAP/NASA](http://wmap.gsfc.nasa.gov/universe/bb_concepts.html)*)
  ------------------------------------------------------------------------

#### Flat Universe

In the early 1990s, one un-answered question in cosmology was what the
ultimate geometry of the Universe was. There were three possibilities
envisioned: positively curved like the surface of a sphere, negatively
curved like a saddle, or flat like a geometric plane. It is difficult to
envision these geometries for our 4-dimensional spacetime, but the image
below shows what they look like for 2-dimensionals.

  -----------------------------------------------------------------------
  ![](media/image37.jpeg){width="5.554166666666666in"
  height="4.981944444444444in"}

  Three possible geometries. The top shows a spherical geometry, which is
  characterized by a positive curvature and is finite in extent. The
  middle image shows a hyperbolic parabolic, or a saddle-like, geometry,
  which is characterized by a negative curvature and is infinite in
  extent. The bottom geometry is a plane, or flat, geometry, which is
  characterized by no curvature and is infinite in extent.\
  *Credit:
  [WMAP/NASA](http://wmap.gsfc.nasa.gov/universe/bb_concepts.html)*
  -----------------------------------------------------------------------

Measurements at the beginning of this decade by balloon-borne
instruments such as BOOMERANG and MAXIMA demonstrated that the geometry
of the Universe is flat. WMAP confirmed these measurements. However,
WMAP was able to go further. With the geometry of the Universe pinned
down, WMAP was able to determine the relative abundances of the
different components of the Universe. WMAP found that normal matter
comprises 4%, of the Universe, dark matter at 23%, and dark energy at
73%.

#### Refined Picture of the Early Universe

After reading this article, one question that might linger is how are
the CMB and inflation related? Indeed, the article discusses how the
current map of the CMB can tell us about the period of inflation, but
the two events -- inflation and the emission of the CMB -- occurred at
different times in the history of the Universe.

The CMB was emitted about 400,000 years after the Big Bang, which is
relatively close to the Big Bang, considering the 13 billion year age
estimate of the Universe. However, inflation occurred within a few
seconds of the Big Bang, so it might be hard to see how the CMB could
tell us much about inflation.

When we discussed inflation in the 1993 edition of Cosmic Times, we said
that it explained some of the problems with Big Bang theory, including
the \"smoothness\" of the CMB. As it turns out, inflation also explains
another problem of Big Bang theory -- how structure in the Universe
formed. Structure came about because of some quantum physics effects,
namely the Heisenberg Uncertainty Principle. Because of this, not all
regions of spacetime experienced the exact same amount of inflation.
Tiny regions that experienced a little less inflation had higher
densities than those that experienced a little more inflation. The
higher-density regions represent places where gravity took hold and
started the process of structure formation.

The WMAP picture of the early Universe can resolve some of these
structures, allowing cosmologists to begin to associate density
fluctuations in the early Universe with grand-scale structures that we
see today.

#### Other resources

The following web pages have more detailed information:

-   [WMAP Website](http://wmap.gsfc.nasa.gov/) -- there are teaching
    materials, animations and further information about cosmology which
    may be useful: http://wmap.gsfc.nasa.gov/

-   [Timeline of the Universe
    Image](http://wmap.gsfc.nasa.gov/media/060915/index.html):
    http://wmap.gsfc.nasa.gov/media/060915/index.html

-   [BOOMERANG](http://cmb.phys.cwru.edu/boomerang/):
    http://cmb.phys.cwru.edu/boomerang/

-   [MAXIMA](http://cosmology.berkeley.edu/group/cmb/index.html):
    http://cosmology.berkeley.edu/group/cmb/index.html

![](media/image2.png){width="5.995833333333334in"
height="1.9444444444444445e-2in"}

### Biggest Mystery: What is Dark Energy?

*The primary message of this article is that dark energy is an as-yet
unsolved mystery in astronomy. When presented with such a mystery,
scientists rally to develop theories to explain the mystery, which is
also the case with dark energy.*

When scientists are faced with a new mystery, they collect the available
data and develop theories to explain the new data. Over time, new data
will contradict some of those theories, and they will drop out of
contentions. Others will be bolstered by the new data. This is the very
process of science. Dark energy is no different from any other
scientific mystery. Astronomers have theories for what it is, and
develop new tests to differentiate those theories.

Astronomers have a few front-runners for what dark energy is, including
the cosmological constant and quintessence, as discussed in this
article. The primary difference between these two models is that the
cosmological constant is a constant energy field filling all of space;
whereas, quintessence allows for changes in the energy field over space
and time.

Over time, new data will help astronomers determine which models work
best. Some theories may require modification while others will be
abandoned. We will all just have to wait and see.

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### Sidebar: Sorting Out the Dark Stuff

*The primary message of this article is that our Universe is made up of
three different components -- normal matter, dark matter, and dark
energy -- but dark matter and dark energy are not the same thing, nor
are they directly related.*

With names like \"dark matter\" and \"dark energy\", it is easy to
confuse the two and to assume that they have some direct relationship to
each other. However, dark matter and dark energy are two very different
beasts. This article is meant to help students differentiate between the
two. Here is a brief description to help:

**Dark matter**: Dark matter is a type of matter that has been
indirectly observed by its gravitational effect on large-scale objects
in our Universe, such as galaxies and galaxy clusters. Without the
gravitational effect of some additional kind of matter, the galaxies and
clusters of galaxies that we see would not be held together. This
additional matter is called dark matter, but it has not been directly
observed.

**Dark energy**: Dark energy is a type of energy that has been
indirectly observed through its effect on the expansion rate of the
Universe. Without dark energy, we would expect that the expansion of the
Universe would be slowing down over time, due to the mutual gravity of
the matter and energy in the Universe. However, the expansion appears to
be speeding up over time, leading astronomers to conclude that there is
\"something\" out there that counteract gravity on the largest scales.
That \"something\" is called dark energy, but it has not be directly
observed.

**What do they have in common?** Both dark matter and dark energy have
only been indirectly observed, and both have the word \"dark\" in their
names.

**What makes them different?** Comparing dark matter with dark energy is
a bit like comparing the earth and sunlight. The two are not the same
type of object. One is a form of matter that gravitates just like any
other matter in the Universe (dark matter). The other is a form of
energy that acts differently from any other energy that we have
encountered in the Universe (dark energy).

It is important to know that dark matter and dark energy are different,
and their presence is seen in different types of observations.
Astronomers know certain characteristics of each, but when it comes down
to it, they aren\'t really sure what either one is yet.

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### \'First Light\' Wins Nobel

*The primary message of this article is that the scientists responsible
for the COBE instruments that measured the spectrum and mapped the
cosmic microwave background back in 1993 were awarded with the Nobel
Prize for physics.*

In the 1993 edition of Cosmic Times, we featured articles on the results
of the COBE mission, which produced a spectrum and mapped the cosmic
microwave background (CMB). By measuring the CMB so accurately, they
proved that cosmology could be a precise science, allowing scientists to
test predictions of different theories of the origin of our Universe.

This article in the 2006 Cosmic Times updates the COBE story with the
announcement of the awarding of the Nobel Prize for Physics to the COBE
mission scientists. This honored the achievements of COBE and its
contributions to the field of cosmology. The fact that this appears in
the same edition as the WMAP results shows the continuity of science,
and how one accomplishment builds on earlier ones.

For more information on the discoveries of COBE, please see the 1993
edition of *Cosmic Times*.

#### Other resources

The following web page has more detailed information:

-   [Nobel Prize for Physics
    2006](http://nobelprize.org/nobel_prizes/physics/laureates/2006/announcement.html):
    http://nobelprize.org/nobel_prizes/physics/laureates/2006/announcement.html

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### Journey to Cosmos\' Dark Heart

*The primary message of this article is that NASA and the Department of
Energy are planning to continue the study of dark energy by launching a
mission to detect a large number of distant supernovae.*

When scientists encounter a mystery, it is in their nature to seek out
an answer. Dark energy is one of the biggest mysteries that modern-day
astronomers have faced, so they want to study it further. Agencies that
run missions and telescopes, like NASA and the Department of Energy,
respond by allocating funds to develop new technologies and to refine
old technologies to study the mystery.

The first hints of dark energy came with observations of supernovae
billions of light-years from Earth. One way to continue studying dark
energy is to observe a larger number of supernovae across the Universe.
That is the plan of JDEM, though the exact details of the mission have
not yet been determined.

#### Process from mystery to mission

This article can be used to illustrate the process that NASA goes
through to develop a mission. Long before a satellite is launched, a
NASA mission begins with a question that astronomers want to answer.
Some questions that have driven NASA missions include, \"What powers a
gamma-ray burst?\" (Swift), \"How is the cosmic microwave background
distributed across the sky?\" (COBE and WMAP), and \"What is the nature
of dark energy?\" (JDEM). With a question in hand, astronomers determine
the types of information they need to begin to answer the question. In
response, NASA solicits the astronomical community to submit mission
concept ideas. Teams of astronomers and engineers write proposals for
telescopes and instruments that they believe will provide the
information necessary to answer the question. These proposals have to
demonstrate how each proposed mission concept would answer the question,
and why a particular method might be better than others.

Using a mission concept, or a combination of mission concepts, NASA then
develops a mission plan. NASA invites its own teams, teams from
University laboratories, other government agencies, and industry (i.e.
companies outside of the government and Universities) to write proposals
to build the telescopes, instruments and spacecraft based on the mission
plan. The teams that participate in the mission are chosen from this
competitive process based on the team with the best combination of
qualifications and skills to get the job done with a given budget.

Usually, construction of the flight instruments, telescopes, and
spacecraft doesn\'t take place until years after the initial question
was posed. Once construction starts, it can take another several years
to complete. Each group is responsible for testing their own
contributions to the final spacecraft, but NASA will also test the
spacecraft once it is assembled into a complete mission. Only then will
it be launched into space.

The process from a question to the launch of a mission can take 10 years
or more (usually more). As of late 2008, JDEM is still in the
mission-planning phase. If all goes as planned, JDEM may launch in a
decade, with its first science results returned a year or so later.

#### Other resources

The following web page has more detailed information:

-   [JDEM Program](http://universe.nasa.gov/program/probes/jdem.html):
    http://universe.nasa.gov/program/probes/jdem.html