Source: TOI from 2012
NEW DELHI: The full moon on Friday is going to be special. It will be what is called a ‘blue moon’, that is, the second full moon in a month. A blue moon is relatively rare, occurring once in about 2.5 years. It happens when a year has 13 full moons instead of 12.
So, is a blue moon bluer than usual? No, the origin of the name is rather arbitrary. According to some accounts, the name first cropped up in a farmer’s almanac. The almanac commonly gave each of the 12 full moons of the year a name. In years when there were 13 full moons, the editor called the extra full moon a blue moon. The next blue moon occurs in July 2015.