total lunar eclipse december 2010

This eclipse is supposed to be one of the best ever. What makes this years’ eclipse so special is the fact that the moon will be very high in the sky and so the eclipse will be seen from coast to coast. (And as Trish of points out in a comment below, it is the first total lunar eclipse to occur during the Winter Solstice since 1378!)

Lunar eclipses always occur at full moon when the moon is behind the Earth from the sun and the Earth’s shadow is cast upon the moon. Therefore, both lunar and solar eclipses can only occur when the Earth, Sun and Moon are directly aligned.

Why Will the Moon Look Copper?

Theoretically, the moon should disappear from sight during totality, since it is completely in the Earth’s shadow. But in this eclipse, the moon will become a gorgeous copper color because of the Earth’s atmosphere. (If the Earth had no atmosphere, the moon would be completely dark during an eclipse. The red coloring arises because some sunlight still reaches the moon. Only direct sunlight is blocked. However, for the light that does manage to reach the moon, it must pass through a long and dense layer of the Earth’s atmosphere, where it is scattered. Shorter wavelengths are more likely to be scattered by the small particles, and so by the time the light has passed through the atmosphere, the longer wavelengths dominate. This resulting light we perceive as red.)