# Presentation: 376443

## Edited: Ruth Petersen

-  The Bowl of Night

-  Mr. K., NASA/GRC/LTP

***Edited: Ruth Petersen***

**Notes:**
The Bowl of Night
-THE TITLE-
Awake! for morning in the bowl of night
Has cast the stone which sets the stars to flight.
And lo! The hunter of the east
Has snared the Sultan’s turret in a noose of light!
										(From: The Rubaiyat of Omar Khayam, trans., E. Fitzgerald.)

## Slide 2

**Notes:**
When we peer into the sky, whether by day or night, we see marvels. Our imaginations soar, and our pulse quickens. In this series, we will explore many of these marvels and discover what science and philosophy have to say about them.
Let’s begin with the most prominent object in our sky, the sun!

## .

***.***

**Notes:**
Seen from earth, the sun may take on many different aspects, from a hot, bright orb in the middle of a summer afternoon, to a gauzy mother-of-pearl luminescence in moderate to heavy overcast. The light and dark of sunlight playing through trees or modern cities is often the object of artists and photographers. The beautiful shades of blue and green and red and orange that color our sky comprises sunlight that has been scattered – i.e., “thrown” about – by the molecules and dust in our own atmosphere. Sometimes, special conditions prevailing in the atmosphere add beautiful phenomena to the sun’s more “routine” daily appearances. Here, sunlight that is being scattered in the semi-cloudy atmosphere of dusk has produced an optical phenomenon know as a sun pillar.

## Slide 4

**Notes:**
Our sun reveals many unexpected features when sight is aided by the telescope and the camera. The photosphere, the visible optical surface of the sun, is a region of incessant activity and turbulence, often erupting in flares (white bands) or prominences (dark bands and eruptions near the limb). The photosphere is not a physical surface. It is an optical surface, which means that the sun goes from being opaque to transparent without there being discontinuity, similar to the “surface” of a cloud in the summer sky through which birds and airplanes fly without the slightest bump.
Matter is ejected from the sun during flares and solar eruptions, often in lethal doses, and passes at high speed through and finally out of the solar system. The matter is in the form of an electrically charged gas called a plasma. But whether the sun is active or quiescent, its attenuated atmosphere extends far beyond the orbits of the known planets. In fact, the planets constantly move through the solar atmosphere in their yearly travels around the sun. In the vicinity of the earth, the solar atmosphere, streaming outward from the sun and interacting with earth’s magnetic field, is called the solar wind.

## Slide 5

**Notes:**
Seen in soft X-rays, the sun again presents startling new features. Here we see that the most energetic regions of the visible sun are associated with the great solar eruptions (cf., previous picture). By observing the sun in different wavelength regions of the electromagnetic spectrum (composed of radio and television waves, infrared, ultraviolet, X and gamma rays, and small portions of visible light), we learn about the many and various physical and chemical processes that occur throughout the sun, even those that occur deep within the core of the sun, almost a half million miles beneath the photosphere.

## Slide 6

**Notes:**
From the vantage point of low earth orbit (altitudes up to 200-300 miles), the sun shines like a baleful yellow-green eye in the eternal night of the heavens. Here, Space Shuttle astronauts, working in the payload bay, must use special equipment to protect themselves from solar heating and special visors to protect their eyes from the intense solar light. The Space Shuttle itself is equipped with special reflective paints and surfaces and is flown in carefully prescribed “modes” to manage the thermal energy from the sun. In the “skewer” mode, for example, the Shuttle is slowly rotated to even out the heating, much the same as a slab of meat on a spit in a rotisserie. On the earth’s surface, sunlight is modified by the atmosphere; in space, it is not. 
The sun also spews out vast quantities of electrically charged particles. On the earth’s surface, and in low earth orbit, the earth’s magnetic field acts very efficiently as a shield against these particles. Once outside this protective cover, however, new precautions must be taken to protect astronauts from absorbing lethal doses. Earth orbital missions (and eventually, piloted interplanetary missions) are planned around periods of intense solar activity to minimize overall radiation exposure, both inside the spacecraft and out.

## Stars - Other Suns!

***Stars - Other Suns!***

***1. Star Colors***

**Notes:**
Our sun is a typical main sequence star. Thus, it is a ‘nominal’ star, akin to an average person in a community of people. Some stars are giants. Compared to the sun, some stars are dwarfs. And some stars travel in tandem with other stars in strange groupings concocted by their mutual gravitational fields.
Of the myriads of stars that we can see on any clear night, one sweeping statement can be made, “All stars are suns, burning nuclear fuel like our sun and generating their own intense light that shines out across the cosmos.” But here the similarity ends. 
Stars may vary greatly in size, age, and temperature. Size, as measured from earth, is a function of brightness and distance. Temperature is indicated by color. And age is a function of mass and temperature. The hotter, heavier stars, on the average, are also the shorter lived. Stars may also vary in terms of whether or not they possess planetary systems.  And if they do have planetary systems, there are variations in how extensive those systems are and whether or not life is present within them. The NASA Hubble Space Telescope has enabled astronomers to confirm, for the first time, the existence of extra-solar planets.

## A Star Thermometer

***A Star Thermometer***

**Notes:**
Stars shine because of thermonuclear reactions being sustained deep within their cores. In our own sun, hydrogen is being converted into helium at a prodigious rate. Some stars manufacture still heavier elements in their cores. In fact, all elements heavier than hydrogen were manufactured within the cores of stars in ancient time, then redistributed throughout the cosmos when the stars died and released their individual hoards. Thus, you, me, and everything around us is literally made of star-stuff! I wonder if the writer of the old hit tune Star Dust ever imagined such a thing!!!
Stellar core temperatures usually run at millions of degrees K. The visible surfaces (photospheres) are much cooler, ranging in the thousands to tens of thousands of degrees K. A quick observational rule of thumb regarding star temperatures is: the bluer, the hotter; the redder, the cooler.

## Orion - the Hunter

***Orion - the Hunter***

***Betelgeuse***

***Rigel***

**Notes:**
Orion, the mighty hunter, provides a textbook-in-miniature of star colors and star sizes. The immense Betelgeuse is an old, cool, red, giant star that is near the end of its stellar life. If Betelgeuse were to replace our sun, its photosphere would extend beyond the orbit of Mars. At the opposite corner from mighty Betelgeuse is the younger, hotter, blue, super-giant star called Rigel. 
Numerous other stars shine in and around the vicinity of Orion. In the sword of Orion is a beautiful gaseous nebula, the birthplace of innumerable stars yet to shine in the heavens of the future. The nebula shines brightly because of the hot, young stars already embedded within it.

## Star Brightness

***Star Brightness***

**Notes:**
That we can see stars at all is one of the great marvels of the cosmos, especially when you consider the distances involved. If we built a scale model in which our sun were reduced to the size of a single grain of salt, the next closest star, Alpha Centauri, would be over 15 miles away! Our own galaxy, the Milky Way, would have a diameter twice the distance from the earth to the moon!! One Important conclusion may be drawn from this observation (a conclusion so obvious as to be almost routinely overlooked): space is transparent.
Astronomers have many ways of measuring distances to the stars. The ancients believed that stars that appear bright are closer than stars that appear relatively dim—a simple rule that is not at all true. 
All stars are not the same. Some stars are extremely bright, while others are so dim as to almost defy detection.

## Star Brightness:

***Which do You Think is Brighter?***

**Notes:**
This little thought experiment underscores the care which must be exercised by astronomers in estimating star distances. Imagine that the bright star is a searchlight, and imagine that the dim star is a lit match. Ask yourself how each configuration would appear if you were the earth.
One means that astronomers use to locate “nearby” stars (say within 50 light years) involves parallax--the apparent shift in the position of nearer objects relative to farther objects as the earth moves around the sun. More subtle methods must be employed, however, for more distant objects...

## The Moon - Our Satellite

***The Moon - Our Satellite***

**Notes:**
OK. Now, let’s take a look at our own satellite, the moon. The moon has no atmosphere--no wind, no rain, no erosion. So the surface that we see is essentially unchanged from the most ancient times. 
The moon wears its history on its surface for all to see. Of the many outstanding features the moon presents to us each night, the dark maria once thought to be oceans (hence the name, maria, Latin for ocean, and the root of such words as mariner), the bright lunar highlands, and the ubiquitous craters are the most prominent. The craters were formed in the earliest developmental phases of the solar system, when the rocky debris left over from building the planets literally rained down on everything. The maria were formed at a later epoch, when an event of unknown origin caused vast quantities of lava to flow and solidify across the earthward face of the moon. (The anti-earthward face shows no evidence of maria at all.)
The most prominent crater of all is Tycho (named for the famous Danish astronomer, Tycho Brahe), a bright “rayed” crater formed in recent times, as geological times are measured. The bright rays comprise material thrown up and out by the impactor. This material rose up in a ballistic plume, then gradually settled back to the lunar surface forming the rays.

## The Moon

***Sun***

***The Moon***

**Notes:**
The phases of the moon are mysterious, until we realize that the earth and moon are both lit by the sun. The moon travels around the earth every 28 days or so, revealing more or less of its lit daylight face for us to see on any given night.
The motion of the moon around the earth also accounts for the change in the time of moonrise from night to night. Follow the various positions of the moon relative to the earth in the drawing above, and the phases and changes in the time of moonrise will become apparent. 

## How Things Move:

***The MOON***

***West***

***East***

**Notes:**
The orbital motion of the moon around the earth may be observed by noting the position of the moon relative to a nearby “fixed” star from night to night. As the moon moves eastward* in its orbit, it may be seen to travel past the star and to change phase. The universe is, after all, a very orderly place!...
--------—--------
*The apparent east-to-west movement of the moon on any particular night is due to the earth’s rotation. When we observe the moon, we must always remember that we are seeing the combined effects both of the earth’s rotation around its own axis and the moon’s revolution around the earth!

## Edited: Ruth Petersen

-  The Bowl of Night

-  Mr. K., NASA/GRC/LTP

***Edited: Ruth Petersen***

**Notes:**
The Bowl of Night
-THE TITLE-
Awake! for morning in the bowl of night
Has cast the stone which sets the stars to flight.
And lo! The hunter of the east
Has snared the Sultan’s turret in a noose of light!
										(From: The Rubaiyat of Omar Khayam, trans., E. Fitzgerald.)

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***Day 2: The Solar System***

**Notes:**
The sun presides over a family of planets, moons, rings, asteroids, comets, dust, and radiation, collectively known as the solar system. In this section, we will examine the planets, some of their moons, and two recently visited asteroids...

## Slide 17

**Notes:**
The sun contains more than 99% of the entire mass of the solar system. The planets circle it endlessly in its immense gravitational field. Here we see the planets and the sun shown in scale of size. The distances between are not to scale, however. The distances would be many, many times greater than shown here! Earth would actually be more than 180 feet from the sun, and Pluto would be 1.4 miles away!!!
The four inner planets, including our own earth, are called “terrestrial.” All four have solid surfaces like the earth; three of the four have atmospheres, and two of the four have moons. The next four planets are called the “gas giants.” Their apparent surfaces are actually the tops of immense cloud systems that hide an unknown interior, which may or may not include a solid surface. The last wayward little world is Pluto. It is in a class of its own. Some think that Pluto may be a moon that escaped one of the giant gas planets ages ago in a disaster whose evidences are all but lost to modern astronomy.

## Which finally cleared out to leave just the Sun & Planets (and their moons, etc.)

***Which finally cleared out to leave just the****** ******Sun & Planets ******(and their moons, etc.)***

_***Formation of the Solar System***_

***It began with a****** ******Nebular Gas Cloud***

***From which developed****** ******Proto-Sun & Planets***

***From which came the****** ******Sun, Planets, & ******Debris***

**Notes:**
The formation of the solar system is, and always will remain, a matter of theory. The prevailing scientific theory is that the sun and planets united out of an ancient nebular gas cloud. Similar clouds may be seen scattered throughout the cosmos today, some apparently giving rise to new generations of stars and (presumably) star systems of their own (cf., the Orion Nebula). 
There must have been considerable debris left over from the formation of the sun and planets. This debris is believed to have left behind a variety of telltale signs. The cratered surfaces of solid planets and moons and the ghostly comets are two such signs that provide tantalizing clues to the process in which the solar system was formed, a process that is ancient beyond imagination.

##  Rocky Matter ...

*** ******Rocky Matter ...***

***What do you see happening here?***
***What do you think that the end result will be?***
***Can we see evidence of this kind of bombardment today?***

**Notes:**
During the early stages of planetary formation, as the masses of planets were increased by the collection of surrounding interstellar gases and objects by gravity, solid debris literally rained down on the developing surfaces of the semi-molten proto-planets and formed craters. How many times must the primitive planetary crusts be disrupted by this “bombardment”?
As the solar system cleared out and things gradually cooled down, the debris became depleted so that, long before the present era, large-scale impacts became a rare phenomenon. That impacts still occur, however, is evidenced by such features as Meteor Crater in the state of Arizona, believed to have been formed somewhere within the last 100,000 years of geological time. Note the road leading to the crater in the upper right of the picture. 
Future impacts, though still rare, are considered sufficiently probable--Hollywood has actually used the theme in several recent box office hits.

## Slide 20

**Notes:**
This is an animation of an impact on the surface of Mercury, the little world closest to the sun.

## Slide 21

**Notes:**
If Venus were subject to impacts during its formation, the evidence is hidden beneath an immense system of planet-encircling clouds. Venus has a planetary climate radically different from that on earth. For reasons unknown, an atmosphere almost 100 times as dense as earth’s at the surface developed and then trapped and held enormous quantities of the sun’s heat in a run-away greenhouse effect. Radar imagery of the surface, taken through this opaque shroud, does reveal a tortured surface abounding with eroded craters and active volcanoes. Perhaps these volcanoes are responsible for the high sulfur content of Venus’ atmosphere. 
Acid rain is a frightening reality on Venus. The sulfur reacts with other elements to form sulfuric acid, which rains down continuously on Venus’ surface and is capable of disabling any spacecraft, unfortunate enough to land there, well within a day.

## Slide 22

**Notes:**
The surface of Venus, as seen by radar, presents tantalizing clues to a complex, dynamic landscape, forever hidden from optical telescopes by a blanket of dense, reflective clouds. Here we see vast ocean-like basins (blue), continental masses (green and brown), and mountainous highlands (white). Other, more detailed images reveal an active surface, swept by dense, hot winds, washed by corrosive sulfuric acid rains, and torn by continuous volcanic activity.

## Slide 23

**Notes:**
Our own earth presents its own complex set of phenomena. Early students of the earth have been confined to observing its surface, digging somewhat into its crust, diving small distances into its oceans, and/or climbing its mountains. With the advent of modern technology, our ability to penetrate into and above the earth is almost limitless. Astronauts who have seen the earth from space have been moved by a sight that many claim has changed their lives. In all the cosmos, this fragile, tiny world is home to the entire human race, and to a dazzling array of flora and fauna. All that we know, all that we have experienced, all that we have seen, touched, tasted, heard, felt, is here, on what one astronaut affectionately christened, “that beautiful, blue gem.”

## Earth as Seen from Space

**Notes:**
The earth presents a wonderful diversity of natural and artificial features. If you were a visitor from another star system seeing earth for the first time, what would you conclude from images such as these?

## Slide 25

**Notes:**
It is only in this most recent era of human history that we have seen our world and her moon from a cosmic perspective. This image was taken by cameras aboard the Galileo spacecraft, on its way to a rendezvous with mighty Jupiter after a complex series of gravity-assisted maneuvers involving the Earth and Venus...

## Slide 26

**Notes:**
Of all the worlds that we may one day visit, our moon is the only place other than earth on which humanity has walked thus far. The Apollo Missions were the crown jewel of the twentieth century, a century that will be remembered as much for its achievements in space and biology as it will for its formidable weapons of war and destruction.

## Slide 27

**Notes:**
As humanity peers longingly into space, its sights settle on Mars as the next most likely human destination. Once thought to be similar to Earth, Mars has challenged us throughout time--from Ancient Rome, where it was revered as a war god, to the present, in which it has been subject to endless speculation, especially concerning the presence of living organisms on its surface. It has presented humankind with an ongoing celestial mystery that has only recently been touched physically and up close by:
two Viking Landers
an orbiter in the 1970’s
Pathfinder in 1997
a variety of other, more recent orbiters. 
The most recent exploration of Mars (MGS) has now provided startling new evidence that conditions once existed there (and may still exist in deep geological layers) that could support life as we know it. Whether life actually was or is there, however, is yet to be determined.

## Slide 28

**Notes:**
Mars is a world with a checkered geological past. The Tarsus region on Mars stands significantly above the average geoid (i.e., the equivalent of Martian sea level). This region is clearly marked by four immense shield volcanoes, the largest observed anywhere in the solar system. To the east of Tarsus is the great surface fault known as the Mariner’s Valley (the Martian Grand Canyon), named for the Mariner spacecraft by which it was first observed. The origin of Tarsus is being studied. One possibility (certainly not proven!) is that Mars was struck at some time in its past by a large body--an asteroid, perhaps, or a large piece of debris loosened after the early stages of planetary formation. The Helles basin, near the point on the exact opposite side of Mars from Tarsus, may be the scar of just such an impact.

## A Day to Remember!

***A Day to Remember!***

**Notes:**
This animation is a crude attempt to visualize an impact event on Mars that may forever have changed its character as a planet. Remember that such an impact is not a proven fact, but is only a theory, a theory that allows us to visualize how Tarsus and its associated surface features came to be.

## Mars

***Mars***

***Tarsus & Mariner’s Valley***

***Tarsus***

**Notes:**
In the same image of Mars that was shown earlier, the major features associated with Tarsus are labeled.

## Slide 31

**Notes:**
Dogs have flees upon their backs to bite ‘em.
Big flees have littler flees, and so, ad infinitum...
													(Children’s nonsense poem.)
Astronomers have speculated about whether moons might not have their own moonlets circling them. Although no such moon/moonlet system has yet been discovered, during its passage through the asteroid belt, the Galileo spacecraft caught this image of the asteroid Ida and its own tiny moonlet Dactyl. The feather-light gravity with which Ida holds its little moonlet, though extremely slight, is sufficient enough to keep Dactyl in a permanent (if somewhat irregular) orbit around Ida. 

## Slide 32

**Notes:**
Also photographed by Galileo is the asteroid Gaspra. Note that on this image, as well as the image of Ida, craters are very evident, providing additional evidence (to that already obtained from the surfaces of planets and their moons) that bombardment by planetary debris was indeed everywhere throughout the early solar system.

## Slide 33

**Notes:**
The next largest object in the solar system after the sun is Jupiter, which is a massive mix of poisonous gases. Jupiter turns once on its axis in a mere ten hours. This rapid rotation causes the gases to be whipped into turbulent zonal bands, each with its own chemistry and weather. 
The great red spot shown here is a powerful cyclone that was first observed some 300 years ago by Galileo, the Italian scientist-philosopher who introduced the use of the telescope into astronomy. The spot is measured in distances that exceed the size of the entire planet earth. Above and below the spot, evidence of large scale turbulence is easily observed. The white spots seen below the red spot are counter-rotating storm cells. These cells may as short lived as a few hours, or may last for weeks or months.

## Slide 34

**Notes:**
Jupiter has a fantastic system of moons, similar to the sun’s family of planets. When Galileo first observed Jupiter with his small 7-inch refracting telescope, he realized that Jupiter and its moons provide a model, in miniature, for the sun-centered solar system proposed posthumously by Copernicus. His attempts to promote a sun-centered point of view, however, eventually led to his arrest and detainment by the Church. The authorities of his time were not yet ready to give up the favored Greek theory that the earth is the center of the universe.
Here we see Io, one of the four Galilean moons. Io is, perhaps, the most volcanically active object in the solar system. It is tortured by gravitationally-induced tides from Jupiter (to which it is very close) and Jupiter’s inner moons. This incessant stressing and straining keeps it hot and active. Additionally, the sulfur and gases released from Io’s volcanoes form an immense cloud that follows Io in its orbit around Jupiter. The cloud conducts gigantic electrical currents between itself and the Jovian poles. Radio noise from these currents is easily detected by moderate-to-large radio receivers on earth.

## Saturn & Two Moons - Voyager

***Saturn & Two Moons - Voyager***

**Notes:**
Beyond Jupiter, in the whispering silence and mind-numbing cold of deep space, reigns the planet Saturn, attended by its own system of moons and by an extensive system of rings. (Two moons can be dimly seen in the image above and are marked with arrows.) 
The rings are believed to be made of individual chunks of rock and ice, ranging in size from grains of dust to orbiting Mt. Everest, each traveling in its own Keplerian orbit around Saturn. Recent imagery of the rings (cf., Voyager spacecraft data) has turned up complex dynamic phenomena that will probably defy explanation for years to come.
One theory is that the rings may be the remains of a primitive moon whose orbit simply brought it too close to Saturn. The resulting tidal forces may have literally ripped the poor moon apart. Time and physics then distributed the remains in the rings we see today.

## Storm on Saturn - HST

***Storm on Saturn - HST***

**Notes:**
Saturn has an active meteorology like Jupiter. Here a cyclonic storm can be witnessed near Saturn’s equator.

## Slide 37

**Notes:**
Uranus is the bluest object yet seen in the solar system. Virtually featureless, this gas giant, never-the-less, holds baffling secrets beneath its immense cloud blanket. It is possible that Uranus possesses an ocean thousands of miles deep. The spin axis of Uranus is tilted at the almost impossible angle of 104 degrees, and its powerful magnetic field is in a state of surprising disarray. Ages ago, Uranus may have experienced a shattering disaster from which it is still attempting to recover. Could little Pluto have once been a moon of Uranus that was thrown free and put into an orbit of its own? This question, though tantalizing, is also highly speculative. Years of research are still required to gain even a moderate understanding of this beautiful blue gas giant.

## Slide 38

**Notes:**
Neptune is also a blue gas giant world. Here, encircled by wispy white ammonia clouds, is the great blue spot, first observed by Voyager. The great blue spot is a cyclonic storm that spins like a frictionless bearing in the absolutely frigid atmosphere of Neptune.
It is interesting to note that Voyager provided photographic evidence that all four gas giants have ring systems. None, however, is as extensive as that of Saturn.

## Slide 39

**Notes:**
And finally...at the very outskirts of the solar system, Pluto and its lone moon, Cheron, keep a lonely vigil. An astronaut on the frozen surface of Pluto would see the sun as no more than a bright star in an eternal night of stars. Little is know of Pluto at this time--it awaits exploration by future generations of scientists...

## Edited: Ruth Petersen

-  The Bowl of Night

-  Mr. K., NASA/GRC/LTP

***Edited: Ruth Petersen***

**Notes:**
The Bowl of Night
-THE TITLE-
Awake! for morning in the bowl of night
Has cast the stone which sets the stars to flight.
And lo! The hunter of the east
Has snared the Sultan’s turret in a noose of light!
										(From: The Rubaiyat of Omar Khayam, trans., E. Fitzgerald.)

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***Day 3: The Universe***

**Notes:**
Beyond the narrow confines of our solar system lies all the rest of cosmic space, filled with unimaginable mysteries. At the largest scales discernable with our small earthbound instruments, there is evidence of organization. Stars are organized into galaxies; galaxies are organized into clusters; clusters are organized into still larger systems.  These systems merge, finally, with a thinly spun distribution of matter, seen at the largest scales yet observed (perhaps a cosmic echo of the turbulence present at the very beginning).

## Which finally cleared out to leave just the Sun & Planets (and their moons, etc.)

***Which finally cleared out to leave just the****** ******Sun & Planets ******(and their moons, etc.)***

_***Formation of the Solar System***_

***It began with a****** ******Nebular Gas Cloud***

***From which developed****** ******Proto-Sun & Planets***

***From which came the****** ******Sun, Planets, & ******Debris***

**Notes:**
Let us return for a moment, to the more familiar territory of our solar system and work our way outward. Recall that the formation of the solar system is, and always will remain, a matter of theory. The same is true of the cosmos. We have already stated that the prevailing scientific theory regarding the formation of our solar system is that the sun and planets formed out of an ancient nebular gas cloud. Similar clouds can be seen scattered throughout the cosmos, some apparently giving rise to new generations of stars and (presumably) star systems of their own (cf., the Orion Nebula). 
The cratered surfaces of solid planets and moons and the ghostly comets, provide tantalizing clues to the processes during which the solar system formed. Similarly, the cosmos is thought to have begun with a singularity (often called the big bang), a physical and mathematical impossibility that we can only approach in thought. From the initial singularity, the cosmos expanded outward, going through a number of stages and phase changes, all dictated by theory, arriving at the present stage, and proceeding to an uncertain end. Relativistic astrophysicists have worked their way through dense mathematics, building models that extend all the way back to 10-43 seconds after the singularity.

## Slide 43

**Notes:**
Let us return again to our solar system and its sub-stellar neighborhood. According to the brilliant theorist Jan Oort, along with the rocky debris that bombarded the proto-planets, there also exists a cloud of residual matter that is primarily ice and dust.  The residual matter is the light stuff that was present in the proto-nebula and that was blown away by the pressure of sunlight as our sun began to burn more and more brightly. Today, this loosely-bound fluff orbits the sun in a region that stretches halfway to the next nearest star. This Oort Cloud is believed to be the source of the comets that occasionally visit our own inner solar system neighborhood.

## Slide 44

**Notes:**
Comets are magnificent wisps of virtually nothing with tails that extend for millions of miles under the pressure of sunlight--a mighty spectacle! In 1910, our earth passed directly through the tail of Comet Halley. Despite predictions of doom, the appointed night came and went without even the most sensitive instruments registering anything at all. 
Around that same time (1911 or 1912), another comet might have actually struck the earth in a remote region in Siberia known as Tunguska (a vast, insect-infected tundra). Despite an impact heard halfway around the world, explorers who later entered the region (circa 1935) found no evidence of a crater. What they did find, however, testifies to the energy that ‘virtually nothing’ can carry. Trees were laid out flat for a radius of over 300 miles around (what is assumed to be) ground zero. It is believed that the wispy cometary nucleus (mostly loosely packed snow, ice, and dust) entered the atmosphere at many tens of thousands of miles per hour and exploded due to the abrupt and intolerable thermal stresses. 

## Slide 45

**Notes:**
Within the galaxy itself, astronomers find smaller star groupings, including binary stars, multiple star systems, and open and closed star clusters. This open star cluster, the Pieiades, is in the shoulder of Taurus the Bull and may be seen high in the northern sky from late fall through early spring. The stars are all bound by gravity and travel around a common center. They co-exist with a cloud of incandescent gas (seen here as blue halos), from which they are believed to have been formed. The star cluster is made of hot blue stars that will probably burn for a few hundred million years or so. (By comparison, our sun, a relatively cooler yellow-green star, may burn for another 5 billion years or so.) 
The NASA Hubble Space Telescope has found many more such groupings, previously unknown to astronomers, and has also provided the first evidence of other stellar planetary systems! This last discovery is an important step toward answering the question of life in space other than on earth.

## Our Galaxy

***Our Galaxy***

***Stars***

***Gas***

***Dust***

***And more stars...***

**Notes:**
This telescopic image of a tiny sector of our own galaxy, the Milky Way, shows many features typical of those seen scattered throughout the cosmos. These features are being studied by astronomers and astrophysicists who search through reams of observational data and manipulate complex mathematical formulas in their quest to seek ultimate answers from the world of space, time, and matter. 
There is enough raw material in the universe to provide novelty to human observers and thinkers from now to the end of time. Loren Eisely, the philosopher, anthropologist, writer, and poet, was often fond of saying, “Man will never find the end of the road.” We seek a final theory. Perhaps the only true ‘theory’ or model of the cosmos is the cosmos itself. Virtually (if not literally) infinite in extent, it may never be fully contained within the compass of a single human cranium, which is a tiny, yet significant, part of the cosmos. In fact, it may never be fully contained within the collective crania of all humanity, past, present, and yet to come.
But there is no room for despair in these statements. If they are true, scientists and philosophers will have bona fide job security from now to whenever!!!

## Slide 47

**Notes:**
Our own galaxy, the Milky Way, is a spiral galaxy, comprised of approximately 400 billion stars. It has thin spiral arms and a somewhat thicker central hub. In this image, we are looking toward the galactic center (hub) from a vantage point inside one of the spiral arms. The horizontal dark band across the image is due to absorbing matter--dust and interstellar grains--with which the spiral arms abound. 
The galactic diameter is around 100 thousand light years; its thickness is approximately two thousand light years. The Milky Way rotates like a cosmic dinner plate around a vertical central axis with an estimated rotational period of 220 million years. 
The Milky Way galaxy is of moderate size, as spiral galaxies go.  M-31, our closest galactic neighbor, is significantly larger than the Milky Way galaxy. M-31 can be seen throughout the late fall and early spring in the constellation Andromeda.

## Slide 48

**Notes:**
Like the Milky Way, M-31 is also a spiral galaxy. Seen here at a viewing angle of approximately 22 degrees, the spiral structure is fairly obvious. The dark material in the spiral arms are lanes of non-reflecting dust and interstellar grains. The bright, irregular areas in the arms are nebular gas clouds, possibly the birthing grounds of new stars. 
Notice the absence of dust and nebulae in the central hub (bright, central region). The stars in the arms are thought to be a younger population of stars, distinct from those in the hub. (Astronomers use the terminology Population I and Population II.) Notice, also, the satellite galaxies above and below M-31. Our own Milky Way has similar satellites--the two famous Magellanic Clouds that are visible in the southern hemisphere.
Finally, the swarm of little objects around M-31 include globular clusters, gravitationally bound to the main galaxy. (The remaining objects are stars in our own galaxy.) Globular clusters have also been seen and photographed in association with the Milky Way.

## M51, The Whirlpool

***M51, The Whirlpool***

***M83 Spiral***

***M100 - HST***

***M15, Globular Cluster***

**Notes:**
Astronomers have found a bewildering array of galaxies scattered throughout the cosmos. This collage shows four of the more well-known examples. Notice the globular cluster in the upper left frame. M-15 is a member of our own Milky Way system.

## M87 Elliptical Galaxy

***M87 Elliptical Galaxy***

**Notes:**
The elliptical galaxy M-87 may hold an ultra strange object within its mighty heart--a black hole.

## Slide 51

**Notes:**
Black holes are the remains of super-massive stars whose nuclear fires have ceased, and which, therefore, have collapsed inward upon themselves. Some extremely bright short-lived stars, the supernovae, shed much of their mass when they collapse. Others, such as our sun, are small enough not to have to shed any mass at all. These stars simply grow old, dwindle to red or white dwarf-hood and, like old coals in the hearth, glow for a few eons before they simply wink out. 
But super-massive stars may do neither. They may collapse beyond the known boundaries imposed by classical physics, literally tearing themselves outside the “fabric” of space-time and leaving behind an event horizon (the edge of the tear, if you will). They may also leave behind an unimaginable gravitational field--so great, in fact, that, at the event horizon itself, even light cannot escape the gravitational grip. 
Modern physics (Relativity) accounts for such objects; classical physics does not. Material falling into the hole under its relentless gravitational pull, would heat up and glow brightly, revealing the otherwise invisible cosmic black hole. It is possible that the bright object above is the image of just such a phenomenon. Note the slender, threadlike streamers of material that appear to be descending into the ‘hole’ from above. Note, also, the jet of matter extending from the ‘hole’ toward the upper right of the image. Such jets have been seen elsewhere in the cosmos, associated with particular types of galaxies and quasars.

## Why isn’t a Black Hole Black?

***Why isn’t a Black Hole Black?***

**Notes:**
This animation attempts to show how radiation from in-falling matter can render a black hole visible.

## Slide 53

**Notes:**
Some binary stars are thought to have, as one partner, a black hole. In the above images, the tiny object orbiting the blue giant star is a black hole. Though small in size, the radiation pouring out of the black hole due to in-falling matter stolen from the blue star itself, is extreme. 
Astronomers today believe that many such binary objects may contain candidate black holes. The discovery and verification of a bona-fide black hole would be a tremendous affirmation of many important theories in modern astrophysics.

## Slide 54

**Notes:**
The Trifid nebula is a beautiful example of cosmic processes of a much gentler sort. The gases in the nebula are set aglow by excitement from stars embedded within. 
These ghostly clouds are remnants left over from previous generations of stars whose component elements were first manufactured in their thermonuclear cores. Lanes of absorbing dust suspended between the nebula and the earth form branching, dark lanes across the image. These lanes are not part of the nebula proper. 
The colors in the nebula are associated with different excitation states in the component gases and/or different local temperatures. Notice also the star colors in the field surrounding the nebula. These stars, along with the nebula, are all members of our Milky Way.

## Slide 55

**Notes:**
The Great Nebula in the sword of Orion is another birth place of stars. A lane of dark absorbing dust between the Nebula and the Earth forms one of the most famous deep sky objects of all--the Horse’s Head.

## Slide 56

**Notes:**
Another view of the Orion Nebula is united with an image of the Crab Nebula.
Early in the second millennium, a bright new star (Latin, nova stella) was observed and recorded, both in Europe and in China. It lit up the heavens for a while, outshining everything else in the sky, then faded again and disappeared. Centuries later, when astronomers examined that same part of the sky, they found the Crab Nebula. In the heart of the Crab is a strange little object called a neutron star. The neutron star and the nebula itself are all that remain of the original star--a supernova that reached the end of its stellar life and shed its matter long ago. The neutron star--the stuff from the stars core--now spins many times per second on its axis and sends pulsating electromagnetic signals into space. These pulses have earned it the name pulsar. 
When the original star blew, its core collapsed, its outer layers rebounded violently into space, and the reaction from the rebound crushed the core into a state of unimaginable density. (Can you see the evidence of all this violence in the nebula?) The core was crushed to the point that atomic electrons and nuclei were jammed together into a state of matter that modern physicists call degenerate, forming essentially, a planetary-sized neutron in space. A single teaspoonful of pulsar “stuff” would weigh many tons if brought to earth. Astronomers call objects such as the Crab supernova remnants. Thus, old stars replenish the cosmos with a rich variety of new elements, synthesized in their cores during their hot, long lifetimes. This matter will eventually become the fertile ground from which new stars will form.

## Slide 57

**Notes:**
And finally, we look outward into the extreme depths of space and time, using the electronic ‘eyes’ of the NASA Hubble Space Telescope. With the Hubble, we see not individual stars, but individual galaxies. 
The Hubble telescope enables us to see out to distances of 10 billion light-years. Equivalently, we may also say that Hubble enables us to look backward some 10 billion years into cosmic time. Thus, with Hubble, we see about two-thirds of the way back to the original singularity (circa 15 billion years ago). For the first time in human history, we are able to observe cosmic structures and events associated with those distant and ancient epochs and, perhaps, obtain clues to the beginnings of the universe. 
With Hubble, we see an estimated 50 billion galaxies in the observable universe! If each galaxy contains 100 billion stars, then the observable universe contains 5 sextillion (5 followed by 21 zeros) stars! And yet, by contrast, a mere cube of water, one inch on each side, contains more than 600 sextillion (6 followed by 23 zeros) molecules! Thus, if our estimates of galaxy and star numbers are correct, then the number of water molecules in a cubic inch of water rivals the number of stars in the observable universe!!!
How do we deal with such ultimate matters? I suggest that we deal with them with hope, with humility, and with compassion. We are part and parcel of the cosmos. We observe, we think, and we call out with electronic devices. We speculate about our significance in so vast an expanse of creation. We wonder if we are alone. And yet, we are each unique. Like an individual snowflake, or an individual star, there is, nowhere, another exactly like ourselves. Perhaps these great exploits of technology and imagination will ultimately teach us just how truly precious we really are.