The Blue Moon and the Number 13

"Once in a Blue Moon" refers to occasional happenings. A recent posting by Space.com revealed a little history behind the saying. Now, a blue moon is the second full moon in a month. In years past, especially before the calendar was standardized, it had another meaning. During a calendar year, usually there are 12 full moons which means 3 full moons in each of the 4 seasons. Occasionally, a calendar year will have 13 full moons. This means one season has an extra full moon. To keep track of time, the moons within a season were referred to a early, mid and late. A 4th moon appearing in a season created a problem. So the 3rd moon in that season was called a blue moon. This allowed the 4th and final moon to still be called the late moon. This extra full moon created additional problems. Monks who kept track of the calendar found this upset the regular arrangement of church festivals. The extra moon was difficult to predict and consequentially its occurrence disrupted a lot of well laid plans. This is one of the reasons the number 13 is considered unlucky. It was an unlucky monk who had to sort out the remaining festivals and rearrange the church schedule. This year, autumn has 4 full moons. Nov. 21st full moon will be the 3rd. Thus it is a Blue Moon by old standards. So enjoy its light and be thankful for a standardized calendar. (Photo by Astroseti.org)