On Thursday, May 31st, 2007, the Moon will be full again, like it does every 29 days. But according to some traditions, it’ll be a special Blue Moon, since it’s full for the second time in May. The first full Moon occurred on May 2nd, and now, still in May, there’s time for another full Moon.
The concept of a Blue Moon has been around for hundreds of years, but the modern definition appeared in the last century. There was a reference to it in books like the Maine Farmer’s Almanac, and an issue of Sky and Telescope in 1946 entitled “Once in a Blue Moon”.
Does anything special happen to the Moon? Nope, it’s just a quirk of the dates, since 29 days can fit inside the 30/31 days we have in a month.
To complicate the matter, though, there are times when the Moon can look blue. If there are tiny droplets of water in the air, they strongly scatter red and green light while allowing other colours to pass through. A moonbeam passing through a wispy cloud will turn a beautiful shade of blue.
So, tomorrow’s a Blue Moon, but it won’t actually be blue. And the Moon can turn blue, but it doesn’t have to be a full Moon, or a Blue Moon. The Blue Moon isn’t anything special, it’s just a trick of the dates. Did that make any sense?
Original Source: NASA Science Article