A rare drama will play out in tonight's skies: a full lunar eclipse on the winter solstice.
The last one occurred in 1638, according to NASA, and tonight's may be only the second one in the last two millennia.
"Since Year 1, I can only find one previous instance of an eclipse matching the same calendar date as the solstice, and that is 1638," Geoff Chester of the U.S. Naval Observatory, who inspected a list of eclipses going back 2,000 years, said on NASA's solstice lunar eclipse page. The next lunar eclipse on the winter solstice won't be such a long wait, though. It's expected in 2094.
Skywatchers expect the eclipse to occur over a three-and-a-half hour period, starting at 10:33 p.m. PT today and ending 2:01 a.m. PT tomorrow. The Earth's shadow will completely cover the moon for about 72 minutes, according to NASA's eclipse page. The shadow is likely to have a reddish hue.
A lunar eclipse happens when the sun, Earth, and moon align--with the Earth in the middle. By virtue of that placement, there is always a full moon during a lunar eclipse. Unlike a solar eclipse, a lunar eclipse is viewable for quite some time and is safe to view. Tonight's lunar eclipse will be visible across North America.
The last full lunar eclipse occurred nearly three years ago in February 2008. The next full lunar eclipse is expected to occur in 2014.
NASA is hosting several events to give more insight into the full lunar eclipse, including live Web chats today and a live chat with an astronomer during the eclipse.
If you're interested in learning more about the history of lunar eclipses, check out this Wikipedia page. It discusses the first known mention of a lunar eclipse in China in 1136 B.C. and includes other interesting facts about eclipse-related events throughout history.
Further reading: Images: Don't miss the total lunar eclipse