Yesterday was the first of two blue moons. The photo above comes from a very informative piece by Borgna Brunner and Anne Marie Imbornoni on the phenomenon of blue moons.
Although the full moon that occurred Thursday, May 31, 2007, looked like an ordinary full moon, it was actually a bit extraordinary—a blue moon.
What is a Blue Moon?
There are in fact two definitions for a blue moon. According to the more recent definition, a blue moon is the second full moon in a calendar month. For a blue moon to occur, the first of the full moons must appear at or near the beginning of the month so that the second will fall within the same month (the average span between two moons is 29.5 days). May 2007 had two full moons: the first on May 2, the second on May 31—that second full moon was called the blue moon.
Note that the May 31 date applies to most of the Western Hemisphere, including the United States. In the Eastern Hemisphere, the full moon in question occured on June 1. For that half of the world, the blue moon will be on June 30, 2007.
