JACKSONVILLE, Fla. — "Once in a blue moon." You've heard that before, no doubt. And just in case this is your first time around the block, a blue moon occurs when there are two full moons in one month. It doesn't happen all that often - they occur just under every three years. 2.7 to be exact, according to Space.com. Hence the cliche.
But the full moon in May happens on May 18. Meaning, there aren't two full moons in the month of May. But there's a blue moon in May. So...wait a minute. This "blue" means...what?
depicting the location of the full moon in mid-May.
The second meaning of "blue" in this case has to do with the SEASONS. If four blue moons occur in one season, the third full moon in that scenario is ALSO known as a blue moon. Well guess what: four full moons occur this spring. The four full moons have to occur between the equinoxes, so let's check our work.
Equinox: March 20, 2019
Full moon: Mar 21, 2019
Full moon: Apr 19, 2019
Full moon: May 18, 2019 (Blue Moon)
Full moon: Jun 17, 2019
Solstice: June 21, 2019
And there you have it. You may also hear the full moon in May called by the names "hare," "budding," "milk," and "flower" because well, Spring.
The next blue moon CALENDAR-speaking will occur in October 2020.
A very interesting note from EarthSky as well:
"Some people prefer the seasonal definition of Blue Moon because it's based on natural phenomena (equinoxes and solstices) instead of an artificial constraint (calendar month). Normally, a season only has three full moons, but the present season actually has four."
© 2020 Cox Media Group