n March 31st, the Blue Sap Moon will take to the night sky. Not only is this the second full moon of March, but the Sap Moon is also the second Blue Moon of 2018 (a rare phenomenon we haven’t seen since 1999). The Blue Sap Moon is clearly a cool dude/dudette. But you might be wondering: what’s with all the names? What does the Blue Sap Moon mean?
The March full moon is actually known by several different names depending on what region of North America you’re in.
According to The Old Farmer’s Almanac, March’s full moon is usually called the Worm Moon, a name that comes from the Algonquin tribes of New England. They called it the Worm Moon because it’s during March when the soil becomes soft again and worms make their way to the surface. When the worms reemerge, so do the robins and other migrating birds, thus signaling spring has sprung.
But in other regions, the March full moon is called the Sap Moon because it’s around this time of the year when sap begins to weep from maple trees. So when there are two full moons in March, the first moon is called the Worm Moon and the second is the Sap Moon.
Other names for the March full moon include Seed Moon, Plow Moon, Crow Moon, or Crust Moon.
The “Blue” in the Blue Sap Moon’s name signifies that this is the second full moon within a month. The phrase that we’re so used to hearing, “once in a blue moon,” actually came about 400 years before an astronomical Blue Moon was defined. And the definition of a Blue Moon that we know and use today is actually derived from a mistake made by amateur astronomer James Hugh Pruett in a 1946 Sky & Telescope magazine article.