Southern Californian sky watchers were blessed with an amazing total lunar eclipse just before sunrise on Saturday, December 10, 2011. This will be the last total lunar eclipse visible from the west coast until 2014.
The timing of this particular lunar eclipse produced an extremely interesting event known as selenelion. In order to appreciate the unique circumstances that produce a selenelion, it's important to first understand the basic geometry that creates a total lunar eclipse. A lunar eclipse can only occur when the full moon and the sun are aligned 180 degrees apart with the Earth in between. The Earth's shadow temporarily blocks the light of the sun, causing the full moon to darken, and as the moon passes deeper into the the Earth's shadow, sun light refracted by the Earth's atomosphere causes the moon to glow orange. On December 10th southern California sky watchers witnessed the rare sight of a fully eclipsed moon setting in the west as the sun rose in the east - a selenelion. This event lasted only a few minutes, but it was a spectacular sight to see.
