Get Ready for the Blue Moon

For things that don't happen very often, we'll often describe them as occurring "once in a blue moon."

This Thursday will not only mark the end of 2009, but will also provide the second full moon occurring in the month of December. That's right: We've got a blue moon coming up this week.

As the San Jose Mercury News points out, the last month that featured a second full or blue moon was June of 2007.

And News Observer informs us that the last time a blue moon happened on New Year's Eve was surprisingly not too terribly long ago: December 31, 1990. The site notes that the occurrence of a blue moon is something that we will encounter every two and a half years on average.

While the origins of the phrase are not completely clear and are a bit baffling, since it has nothing to do with the color or appearance of the moon, the term has been used to describe both the second full moon contained within the same calendar month as well as the fourth full moon to occur within a particular season, which normally will feature three of the celestial events.

So do a little skygazing this Thursday. It only happens once in a ... well, you know.

Photo courtesy of NASA