December 10, 2011 Lunar Eclipse

Eclipses are among the most awesome spectacles in nature, but somewhat rare occurrences simply due to the large number of factors that have to be just right in order for them to take place. On average, there is a total solar eclipse visible somewhere about every eighteen months. Lunar eclipses are a lot more common, occurring, on average, about every six months.

This year’s last eclipse is a total lunar eclipse on December 10, best visible from Asia and Australia. For people on the west coast of the United States and Canada the eclipse is in progress as the Moon sets, and observers throughout Europe and Africa will miss the early eclipse phases because they occur before moonrise.

The eclipse’s partial phases begin at 4:46 A.M. PST (12:46 UT), when the Moon’s leading edge enters the dark umbra of Earth’s shadow, and the celestial show ends at 8:18 A.M. PST (16:18 UT), when the Moon’s disk completely exits the umbra. Totality starts at 6:06 A.M. PST (14:06 UT) and ends at 6:57 A.M. PST (14:57 UT).

Lunar eclipses occur when a full Moon is exactly on the line from the Sun to the Earth. The Moon is then in Earth’s shadow, or the umbra, and takes on a reddish or orange color. This coloring comes from light refracted around the edge of Earth towards the Moon; it comes from all Earth’s sunrises and sunsets. If Earth’s atmosphere is especially opaque, as happens following a major volcanic eruption, the eclipse can be so dark that the Moon disappears, but this is very rare.

No two lunar eclipses are alike, since there is always some factor that causes variation in the phases, brightness or color; consequently is worthwhile observing each eclipse. One of the best ways to monitor the progress of a lunar eclipse is with binoculars. A powerful telescope will give you a close-up view of the shadow moving slowly over the craters, but with their wide views and sharp optics, binoculars give you a striking perspective on the entire drama of totality.