Are blue moons actually blue?

While the name "blue moon" conjures up a vivid, colorful image, the term actually refers to those times when there are two full moons in a single month; that second full moon is referred to as the blue moon, though its color is likely to be the same as it ever is. It is possible for the moon to have a bluish appearance, but this is usually due to atmospheric changes on earth, such as smoke or ash in the upper atmosphere as the result of fires or volcanic activity.

Blue moons, though not actually blue in color, are somewhat rare. The lunar cycle takes about 29 days to complete, which is shorter than the average earth month, and there are usually just 12 full moons every year. However, every 2 or 3 years, there will be a month that has two full moons, the second of which is known as the blue moon. People have been using the term "blue moon" to describe strange or rare occurrences since the 1820s.