• Today - Friday, August 31, 2012 - features a Blue Moon by the most well-known definition of the term. By popular acclaim, the second of two full moons to occur in one calendar month is called a Blue Moon. Look up! You'll see the full moon shining in the sky from dusk until dawn. Will it look blue in color? No. But many will call it by the name Blue Moon.
• Next year - on August 21, 2013 - we'll have a different kind of Blue Moon: the third of four full moons to fall in a single season. A season is the period of time between a solstice and an equinox, or vice versa. This alternative definition

of Blue Moons is harder to remember, and that's probably why it has fallen out of favor.
• Click here to learn the history of Blue Moons
• Hmm. That seems like a lot of Blue Moons. And doesn't the phrase "once in a Blue Moon" indicate something precious and rare?
• In fact, especially now that there are two definitions for the name Blue Moon, they're not rare at all.
• So how often do we have a Blue Moon by today's definition - two full moons in a single calendar month? In a period of 19 years, there are generally 235 full moons but only 228 calendar months. That being the case, it's inevitable that at least 7 of these 235 calendar months should harbor two full moons. In other words, if you're defining a Blue Moon as the second full moon in a calendar month, you'll have a Blue Moon once every two to three years.

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