Blue MoonPhoto byGetty Images

“Do you see that full moon in the sky tonight? That happens once in a blue moon.”

Scientifically, this happens 7 times in 19 years or about once in 3 years.

A blue moon occurs today, August 19, at 2:26 PM EDT (18:26 GMT). It’s also a supermoon.

I first wrote about this on July 31, 2015. We had blue moons in January and March 2018 and October and November 2020. Blue moons never occur in February, which has only 28 days. The time between two successive full moons is approximately 29.5 days.

A full moon can be considered a supermoon when its orbit is closest to Earth, as in August when the moon is in its elliptical orbit around the Earth.

You won’t see a blue moon again until May 31, 2026; the last time was August 31, 2020. Technically, the full moon occurred at 18:25 AM ET today.

So, what is a Blue Moon?

Blue Moon Definition

It has nothing to do with the color of the moon. Why “blue”? Several folk etymologies suggest it may be a mispronunciation of the disused word “belewe,” which means ‘to betray.’ This may be a reference to the betrayal of the usual idea of having one full moon in each month. Or perhaps it’s the “betrayal” by the Moon of worshipers attempting to determine the position and duration of Lent in the calendar year.

The primary definition of a Blue Moon, according to the now-defunct Maine Farmers’ Almanac, is:

the 4th occurrence of a moon in a 3-month season rather than the more regularly occurring 3.

An alternative and more recent definition appeared in a 1943 Sky and Telescope Magazine article, referring to a blue moon as a second full moon in a month. This second definition has stuck due to a Star Date radio show reinforcing it in 1980, a U.S. children’s book, The Kids’ World Almanac of Records and Facts, in 1085, and the popular board game Trivial Pursuit in 1986.

How does a Blue Moon fit into the Calendar?

That’s the problem; there are usually 12 full moons in a year. The aforementioned Maine Farmers’ Almanac posited that a 13th full moon “upset the arrangement of Church festivals.” Some church holidays in the ecclesiastical calendar are tied to the phases of the moon.

Historically, Easter was set – at the church Council of Nicaea in 325 A.D. – to be observed on

the first Sunday after the full moon following the vernal equinox.

Hence, Lent, which is set 40 days before Easter, is also determined by the phase of the moon.

What are other names?

It is also called a Full Sturgeon Moon (if both full moons occur in August), Green Corn Moon, Grain Moon, Full Red Moon, or Strawberry Moon.

Of course, it is also the name of a 1961 #1 hit song by the doo-wop group The Marcels, originally written in 1934 by Rodgers and Hart.

Blue Moon
You saw me standing alone
Without a dream in my heart
Without a love of my own.

Bill Petro, your friendly neighborhood historian