Blue Moon Soon

For the first time in almost twenty years, there's going to be a Blue Moon on New Year's Eve.

Most months have only one full Moon. The 29.5-day cadence of the lunar cycle matches up almost perfectly with the 28- to 31-day length of calendar months. Indeed, the word "month" comes from "Moon." Occasionally, however, the one-to-one correspondence breaks down when two full Moons squeeze into a single month. Dec. 2009 is such a month. The first full Moon appeared on Dec. 2nd; the second, a "Blue Moon," will come on Dec. 31st.


Update....
On Dec. 31st, the Blue Moon will dip into Earth's shadow for a partial lunar eclipse. The event is visible from Europe, Africa and Asia. At maximum eclipse, around 19:24 Universal Time, approximately 8% of the Moon will be darkly shadowed.
Blue Moons are rare (once every ~2.5 years). Blue Moons on New Year's Eve are rarer still (once every ~19 years). How rare is a lunar eclipse of a Blue Moon on New Year's Eve? See the animated preview at SpaceWeather.com

For more on Blue Moons, visit
Science@ NASA