|
Phases of the Moon
So why does the Moon seem to change its size during the month? Well, of course, the Moon isn't changing in size, but because the Moon is revolving around the Earth, we see the Moon differently as the Moon's position changes relative to the Earth. The picture below illustrates how the Moon appears to change as it moves around the Earth. The light we see coming from the Moon is all reflected from the Sun. If the Moon is between Sun and the Earth, there is no reflected light so the Moon is dark. Conversely, if the Moon is on the far side of the Earth, we see a full Moon. A complete cycle of the Moon's phases takes 29-1/2 days [1].
In the figure below, the relative positions of the Sun, Earth, and Moon
are shown using the outer ring of Moon pictures, and views of the Moon from the Earth are shown in the inner ring of Moon pictures.
Click here for enlarged view.
Eclipses
We know that the Earth-Moon-Sun system is always moving relative to each other. We also know that only stars (like our Sun) produce their only light. All other celestial bodies reflect light for us to see or it blocks light. Blocking light is what eclipses are all about. All bodies create a shadow region. If another body moves into that shadow region, there's an eclipse. Below is an illustration of a LUNAR ECLIPSE. In this case the Earth has moved between the Sun and the Moon. If you were viewing this event from the Earth, you would see the Earth's shadow move across the Moon. The Moon would darkening and then brighten again as the Moon moves out of the shadow.
The other type of eclipse is the SOLAR ECLIPSE. In this case the moon moves between the Sun and the Earth. Notice that there are regions of total or annular and partial eclipse. What you would see depends on where you are on the Earth's surface and distance between the Earth and the Moon and the Moon and the Sun. (Remember, NEVER look directly at the Sun.) If the Moon happens to be at it's furthest distance from the Earth, it will not be able to totally block the Sun's light.
Other Influences
Although we often only think of the Moon's gravity or tides when thinking about how the Moon influences the Earth, the Moon's effects are much more far reaching. Over history, especially before electric lights, the phases of the Moon and how much light the Moon reflected has had a huge influence on humans. There has certainly been the spiritual connections to witches and werewolfs and the like, and there has always been folklore about "moon madness" associated with a full moon. People have also planned their socializing about a full Moon because it is much safer to travel when they could see the road. The phase of the Moon is also important for military reasons. If you were a spy, slinking behind enemy lines, would you prefer it to a new Moon or a full Moon? The behavior of nocturnal animals is also influenced by the phase of the Moon. Nocturnal animals are typically much more active when it is a full Moon. What about crime? Smugglers often prefer the dark night of a new Moon. As you can see, the Moon's influence on the Earth is very far reaching.
Miscellaneous Facts
The moon has a diameter of about 2,160 miles (3,478 kilometers). That makes it about one quarter the size of the Earth. The moon travels in an elliptical orbit around the Earth. The average distance between the Earth and Moon is about 248,000 miles or 400,000 km.
The Moon orbits the Earth about every 27-1/3 days.
The Moon rotates about an axis every 27-1/3 days, the same amount of time it takes to orbit the Earth. That's why we only see one side of the Moon.
Activities - Explore how an eclipse works
In a darkened room turn on a bare table lamp, that's the Sun. Use a basketball for the Earth and smaller ball, like a tennis ball or small soccer ball for the Moon. Now simply try to simulate Lunar and Solar eclipses! Move the Earth between the Sun and Moon for a lunar eclipse. Move the Moon between the Sun and Earth for a solar eclipse. You will need to play with the distance between the objects.
Convince yourself that the Moon rotates once each time it orbits the Earth. Rotate a ball representing the Moon around another ball representing the Earth. Keep the same side of the Moon always facing the Earth.
Check out these links for related information about eclipses:
Photos
http://www.comet-track.com/eclipse/eclipse.html
Lunar eclipses
Solar eclipses
Solar Eclipse info.
http://www.mira.org/fts0/sun/079/text/txt001x.htm
Eclipse info.
NASA Goddard Eclipse Page
Kids Astronomy (use the site search for "eclipses")
Other Information
See the Moon or Earth at any day or time!
Misc.
Moon Info.
Tidal forces
Misc. Solar System Info.
More
info on the Earth and Moon
Glossary of terms
Virtual Field Trip
References
- Campbell and Ronald Rood, The New York Public Library Incredible Earth: a book of Answers for kids, Wiley & Sons, 1996.
- Fleisher, Paul, Our Oceans : Experiments an Activities on Marine Science, ISBN 1-56294-575-0, 1995.
| 
