The Blue Moon: Explained
By Scott Cimini on August 30, 2012, 12:00am
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In the 21st century, according to folklore, the name Blue Moon has two meanings. A Blue Moon can be the second full moon in a calendar month or it can be the third of four full moons in a single season.The time between two full moons isn't quite a full month so approximately every three years there are two full moons in one month. When this happens the 2nd full moon of the month is called the "blue moon". The next time two full moons will occur in a month is in August of 2012. On average there's a blue moon every 33 months. Blue moons are very rare because there is a full moon every 29 and a half days. The timing has to be precise to fit two blue moons in a year. People use the term blue moon in regular conversation as well. The term blue moon has taken on the meaning of seldom or absurd. It's even more rare to have the moon actually turn blue or have a blue tint but it still is possible. Volcanic eruptions and wildfires can cause the moon to appear blue if the airborne particles from these events are just the right size. They have to be about 1 micron (one millionth of a meter) wide to act like a color-filter for the moon. Clouds of water droplets, ice crystals or fine-grained sand can do the same thing. Another reason for an odd-looking moon is because our own eyes have automatic 'white balances' just like digital cameras. "If you sit in a cabin lit by an oil lamp (yellow light) for hours and then you step outside, the moon will appear blue until your eyes adjust to being outside" says Atmospheric optics expert Les Cowley.
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