 (Fred Espenak, © 2001, www.MrEclipse.com) A total solar eclipse, photographed at Chisamba, Zambia on Jun. 21, 2001. At the time Espenak took the picture, the Moon had obscured 36% of the Sun’s diameter.
Why There's No Monthly Eclipse
by April Holladay, www.WonderQuest.com
JUNE 30, 2008 Q: Why isn’t there a solar eclipse every month?
-Saima, Islamabad Pakistan
Q: We don’t have a monthly eclipse because the Moon doesn’t revolve around the Earth in exactly the same plane as Earth revolves around the Sun. If it did, then we would have an eclipse at every New Moon (a solar eclipse) and at every Full Moon (a lunar eclipse).
As Earth circles the Sun, it traces an ellipse — almost a circle — in the sky. The Moon does likewise as it circles Earth. However, the Moon’s ellipse lies in a plane about 5 degrees slanted to Earth’s orbit. That little difference matters. Only about one out of six new or full moons produce an eclipse. Half the time the Moon lies above Earth’s orbit (called the plane of the ecliptic) and half the time it dips below. We have an eclipse when the Moon crosses the ecliptic plane or comes close to crossing. Only then can the Moon cast a shadow on Earth (lunar eclipse) or blot out the Sun (solar eclipse).
Further Reading:
Solar Eclipses for Beginners www.mreclipse.com/Special/SEprimer.html
Lunar Eclipses for Beginners www.mreclipse.com/Special/LEprimer.html
Earthview: what causes an eclipse
NASA: Amazing facts about solar eclipses
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