# Presentation: 126596

## Sun, Earth, and Moon

- Lunar Phases
- Eclipses
- Tides
- Celestial Motion

## Phases of the Moon

**The appearance or shape of the Moon gradually changes through the course of a month. This cycle - the cycle of lunar phases, may be explained if we state the following: **
**The Moon is spherical in shape. **
**The Moon is not self-luminous, but rather reflects the light of the distant Sun. **
**The Moon circles the Earth once per month. **

## Slide 3

**Notes:**
The moon appears to change shape over the course of a lunar month (one rotation around the Earth) because, from Earth, we see different parts of the moon illuminated by the sun. Since the moon gives off no light of its own, we rely on reflected sunlight to show us its surface.

## Fun Facts for Lunatics

**Lunar Libration: **The spin of the Moon proceeds at a uniform rate while the orbit is at a slightly nonuniform rate. The spin can get a little bit ahead or behind the orbit. Hence the face of the Moon presented to the Earth rocks back and forth by some 6° each month, a phenomenon known as longitudinal libration.
**The Moon's orbital plane:** The plane of the Moon's orbit is tilted by 5° with respect to that of the Earth's orbit. Hence the rotation axis of the Earth is tilted with respect to the Moon's orbital plane by an amount within 5° of 23.5°, depending on whether the two tilts are in or out of phase. The length of time between moonrise and moonset for, say, a full Moon varies with the season as well. (Also, note the phasing between the two tilts varies continually with time, going full circle every 18.6 years.)
**The variable speed of the Moon:** Like the Earth, the Moon moves in a slightly elliptical orbit as well. Hence, while the average time elapsed from, say, New Moon to First Quarter is 7.4 days, the actual time can be as short as 6.7 days near perigee (closest approach to Earth) or as long as 8.1 days near apogee.

## Moon at Perigee and Apogee

- Distance: 359,861 km

- Distance: 405,948 km

**Notes:**
The moon orbits the Earth in an ellipse. When the moon is closest to us (Perigee), it appears larger. At Apogee (furthest from Earth), it appears smaller. At Apogee, it is too small to cover the entire sun during a solar eclipse so we see only an annular eclipse.

## Eclipses

- Celestial bodies are always “eclipsing” or moving in front of each other.
- Eclipses occur at predictable intervals.
- Other names include: Transits and Occultations.
- Solar Eclipses can be total, partial, or annular

## Slide 7

**Notes:**
During a solar eclipse, the moon passes directly between the Earth and the sun, blocking out the sun as seen from Earth. A path of totality is formed where the moon blocks out the entire sun and observers can see a total eclipse. Outside the path of totality, only a partial eclipse can be viewed. 

## Slide 8

**Notes:**
This graphic illustrates how the shadow of the moon falls on the Earth during a total solar eclipse. Notice how small and narrow the path of totality is.

## Moon's shadow on Earth taken by French cosmonaut Jean-Pierre Haigneré aboard the Mir 

- Moon's shadow on Earth taken by French cosmonaut Jean-Pierre Haigneré aboard the Mir

**Notes:**
Shadow of the moon on the Earth as observed from the MIR space station.

## Slide 10

**Notes:**
This graphic shows the path of totality for different solar eclipses through 2025. Notice there are two solar eclipses that cross the United States (2017 and 2024).

## Slide 11

**Notes:**
Total Solar Eclipse showing the corona and a few prominences off the limb (in red). When the moon blocks the light from the bright solar photosphere, we can see the much dimmer, more subtle evidence of the corona.

## Slide 12

**Notes:**
In a lunar eclipse, the Earth moves between the sun and the moon and casts a shadow on the moon. Lunar eclipses can come in a variety of colors from deep black to rich shades of red. The red coloring comes from light from the sun that is filtered as it passes through the Earth’s atmosphere and is bent toward the moon. That light reflects off the surface of the moon and into our eyes on Earth. Lunar eclipses are only evident when the moon is passing through the Earth’s umbral shadow.

## Slide 13

**Notes:**
Lunar eclipse.

## Slide 14

**Notes:**
Many solar system bodies partake in eclipses, transits, and occultations. Here, Jupiter’s moon, Io, casts a shadow on Jovian cloud tops.

## Slide 15

**Notes:**
Saturn slowly disappears behind the limb of the moon in this video sequence.

## ECLIPSE QUOTES

- Author unknown: Said to refer to the Chinese
- eclipse of 2136 BC or 2159 BC.

**"**On the day of the new moon, in the month of Hiyar, the Sun was put to shame, and went down in the daytime, with Mars in attendance.**"**

- One of the earliest written records of an eclipse of the Sun, on 3 May 1375 BC, found in the city of Ugarit in Mesopotamia.(Reprinted, from *Chasing the Shadow*, copyright 1994 by Joel K Harris and Richard L Talcott, by permission of Kalmbach Publishing Co.

**"**If the Sun at its rising is like a crescent and wears a crown like the Moon: the king wll capture his enemy's land; evil will leave the land, and (the land) will experience good . . . **"**

- Refers to a solar eclipse of 27 May 669 BC.Rasil the older, Babylonian scribe to the king.Quoted in *Historical Eclipses and Earth's Rotation*, by F Richard Stephenson, Cambridge University Press, 1997, page 125.

**"**Nothing can be surprising any more or impossible or miraculous, now that Zeus, father of the Olympians has made night out of noonday, hiding the bright sunlight, and . . . fear has come upon mankind. After this, men can believe anything, expect anything. Don't any of you be surprised in future if land beasts change places with dolphins and go to live in their salty pastures, and get to like the sounding waves of the sea more than the land, while the dolphins prefer the mountains.**"**

- May refer to a total solar eclipse of 6 April 648 BC. Archilochus, Greek poet (c680-640 BC) Quoted in *Historical Eclipses and Earth's Rotation*, by F Richard Stephenson, Cambridge University Press, 1997, page 338. Partly quoted in *Encyclopaedia Britannica CD 98*.

## Slide 17

**Notes:**
In 1973, Fred Espenak photographed this transit of the planet Mercury across the face of the sun. There are about 13 transits of Mercury each century. The next one will occur on November 8th,  2006 and will be visible from the United States.

## 1882 Transit

**1882 Transit**
**(USNO)**

**Notes:**
The 1882 transit of the planet Venus across the sun was viewed by millions of professional and amateur astronomers. This image was taken at the US Naval Observatory.

## Application to Exo Planet Studies

- HD 209458 (mv = +7.7) in Pegasus

**Notes:**
Transits of planets around distant stars are one way astronomers can detect these extra solar planets. As the planet moves in front of the star, a small percentage of the light from that the star is blocked and the light curve (shown at right) dips. When the planet moves off the limb of the star, the light curve recovers. This method is only effective when the plane of the orbit of the planet is in our line of sight. 

This viewgraph depicts real data of a planetary transit around the star HD209458 in the constellation of Pegasus.

## Slide 20

**Notes:**
In addition to transits of stars, planets can be detected by detecting gasses in their much cooler atmospheres. Here sodium is detected in the atmosphere of a planet from Hubble Space Telescope spectral observations. This observation of HD209458 (150 ly away) was the first direct detection of a planetary atmosphere outside our solar system.

## When the moon is at first and third quarter, the gravitational forces of the sun and moon are pulling at 90 degrees from each other. (see the diagram below.) This occurrence yeilds little net tides called neap tides. 

- When the moon is at first and third quarter, the gravitational forces of the sun and moon are pulling at 90 degrees from each other. (see the diagram below.) This occurrence yeilds little net tides called neap tides.

## More Fun Tidal Tales....

- Every few years people that measure such things (chronologists?) need to add a leap second to the year. The Earth's rotation is decelerating at a rate of about 0.002 seconds per day per century.
- The Earth will eventually stop slowing down – when it’s rotation is equal to the moon’s orbital period !!!
- The **Proxigean Tide** occurs when the Moon is at its closest point in its orbit to the Earth and in its New or Full Moon phase. At this time, its tidal effect on the Earth is maximum. The times when this will happen often coincide with major coastal flooding events. Between 1997 and 2020 there will be 102 times when this will happen.
- The moon shows the same face to the Earth because it was deformed by Earth’s gravity when it was still molten. Earth uses this “memory” to grab the moon and slow its spin rate down.

*WHY ?*

## Resources

**Paper Plate Astronomy** 	_[http://analyzer.depaul.edu/paperplate/](http://analyzer.depaul.edu/paperplate/)_
**Solar Events****	****	**_[http://solarevents.org](http://solarevents.org/)_
**Eclipses****	****	****	**_[http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html](http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html)_
**Earth Moon Viewer****	**_[http://www.fourmilab.ch/earthview/vplanet.html](http://www.fourmilab.ch/earthview/vplanet.html)_
**Lunar Posn Calculator****	**_[http://www.fourmilab.ch/earthview/pacalc.html](http://www.fourmilab.ch/earthview/pacalc.html)_
**Lunar Phases, etc.****	**_[http://www.lkwdpl.org/schools/elempath/heavenlymotion/](http://www.lkwdpl.org/schools/elempath/heavenlymotion/)_