Blue Moon

These things only happen once in a blue moon...

There are about 12 lunar cycles in a year. A lunar cycle is 29 days long. In our Gregorian calendar there are 12 months in a year and generally one full moon each calendar month. As a month is longer than a lunar cycle, these extra days accumulate so every 2 or 3 years there is an extra full moon. When this happens there are two full moons in a calendar month instead of one. It is the second full moon of the month that is called the Blue Moon. Traditional Folklore named each of the years twelve moons according to the time of year so the extra moon was called the blue moon so the rest of the moons retained their traditional names.