On Saturday, May 18, you can see a blue moon — but don’t expect it to actually be blue.
The name is just what scientists call an “extra” full moon.
An astronomical season — between solstice and equinox — usually has only three full moons. But when there happens to be a fourth in that period, which occurs about every two and a half years, the third one is known as a seasonal blue moon.
That’s what we’ll be seeing this weekend, and it will be the last one until Aug. 22, 2021.
It’s believed the first reference to this kind of blue moon showed up in a farmers’ almanac during the mid-20th century.
But the term goes back some 400 years, says folklore expert Dr. Philip Hiscock.
Back then, to call the moon blue would have been as absurd as claiming pigs can fly — hence, “once in a blue moon” (or, to be literal, once every two and a half years or so).