Eclipses

Solar eclipses are so incredibly awesome, but they are only possible because of a crazy coincidence. Watch the video Angular Size of the Sun and Moon to see what I mean.
Read 4.7 Eclipses of the Sun and Moon to understand the phenomena of solar and lunar eclipses, including their causes, occurrences, and visibility from Earth.
Watch the teacher video Eclipses to see simulations, images, and videos of both lunar and solar eclipses in action. If you like, you can also play with the Eclipse Shadow Simulator for yourself.
Check out this amazing 5-second time-lapse video Moon Shadow versus Sun Reflection from a geostationary satellite looking back at the earth. It shows the shadow of the moon as it passes over the surface of the earth during a total solar eclipse.
The next total solar eclipse that will be visible in the United States will be on August 12, 2045. Check out this map of the path of totality to see if it will be visible in your part of the country.