Before we get into all that, let’s break down the meanings of the moon’s name. First, the term “ blue moon ” does not mean the moon will appear blue (unfortunately, because that would be cool). You might have heard the phrase “once in a blue moon” to describe something that occurs rarely — well, here’s where that phrase comes from! Usually, there is one full moon per month, and three full moons per season. Any “extra” full moons are called “blue.” This year, we have four full moons in spring instead of the usual three full moons — and, according to the Farmer’s Almanac , it’s the third of these four full moons that gets the special “blue” nickname, though no one is sure why that is.