A Blue Moon

Tomorrow, May 31, 2007, there will be a Blue Moon. When people hear the term, "Blue Moon," most assume that the moon will seem blue. That is not the case. A Blue Moon is when there are two full moons in one month. Because there is a full moon every 29 days, this moth, the last and full moon and the next one (tomorrow) are coincidentally going to occur in the same month.

Image credit: Kostian Iftica
Although the term a Blue Moon should not be taken literally, there are some cases when the Moon actually appears to turn blue. Sometimes when small droplets of water are in the air, they can break down the light that comes from the moon (moonbeam). The moonbeam then turns blue. "Clouds of ice crystals, fine-grained sand, volcanic ash or smoke from forest fires can have the same effect (NASA)." For the effect to happen, the particles from the various substances have to very small, a size of about one micron (one millionth of a meter).

Original Source: NASA Science News