An eclipse is when the moon is directly in-between the sun and earth. There are two types of basic eclipses. There is lunar and solar. There are three basic Solar Eclipses. The Total Solar Eclipse, these happen when the umbra of the moon’s shadow touches a portion of the earth on its surface. There are also Partial Solar Eclipses, these happen when the penumbra of the moon’s shadow passes over an area of earth’s surface. Plus there is the Annular Solar Eclipse, these happen when a part of the surface of the earth is lined up with the umbra of the moon’s shadow because the distance ends up barely out of reach of the earth’s surface. The period and re-occurrence of solar and lunar eclipses is governed by the Saros cycle, approximately 18 years, 11 days, and 8 hours.

The most recent eclipse was on September 22, 2006. It was an Annular eclipse that lasted for 7 minutes and 9 seconds. If you want to see an eclipse you have to be ready because they don’t always last very long. A solar eclipse happens when the moon goes between the earth and sun. They could occur every seven lunar orbits. The umbral shadow, the part where a total solar eclipse can be viewed on earth, and usually less than 100 kilometers in diameter Eclipses, if they are solar or lunar, happen when the earth, sun, and moon are in line. The moon orbits earth every 28 days, why not expect a solar eclipse to happen every 28 days? A lunar eclipse happens in the same time period. This would be the case if the orbit of the moon were the same as the earth’s. But eclipses are rarer than that. The moon’s orbit also has to be at the correct tilt.

Credits:
http://csep10.phys.utk.edu/astr161/lect/time/eclipses.html
umbra pic and solar and lunar eclipse
http://www.scienceu.com/observatory/articles/eclipses/eclipses.html
Helen Hogg pic
 http://www.research.utoronto.ca/edge/winter2000/content5.html