Friday, May 20, 2016

May 19, 2016
By A. J. Burnett

Boston —There are many definitions (click here) for the term "blue moon." This weekend's full moon will be an "old school blue moon."
According to the Maine Farmer's Almanac, a "blue moon" was originally defined as the third of four full moons in one season. Typically, seasons only have three full moons. This year, there are four full moons in spring, and the third occurs this weekend, on Saturday.
The next blue moon, according to this older definition, won't occur until May 18, 2019.
A new definition came into play when an article appeared in Sky and Telescope Magazine in March of 1946. Author James Hugh Pruett mistakenly defined a blue moon as the second of two full moons appearing in the same month, which also happens more commonly. This is the more popular definition used today.
The next blue moon, according to the new definition, occurs on Jan. 31, 2018.