Dec 21, 2009
A lunar eclipse occurs only during a full moon when the moon and sun are on opposite sides of the Earth and all three bodies exist in a straight line. In this configuration the Earth blocks the sun's rays, thus casting a shadow on the moon. The Earth, moon, and sun only rarely line up in this manner because the plane of the Earth's orbit around the sun is different from the plane of the moon's orbit around the Earth. (A plane is an imaginary surface that runs through all the points of an orbit.) Only once every six months or so do these planes intersect, creating the conditions required for an eclipse.
In a total lunar eclipse the Earth's shadow completely covers the moon and the moon seems to disappear from the sky. A total lunar eclipse may last up to 1 hour and 40 minutes.
If only part of the moon is covered by the Earth's shadow, a partial eclipse occurs. It is difficult to...
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