There are two ways to say a full moon is a Blue Moon: the third Full Moon of an astronomical season that has four is called a Seasonal Blue Moon and when a Blue Moon occurs twice in a calendar month, it is the second one.
The Aug.22 full moon is a seasonal Blue Moon.
It will be exactly full (that is, directly opposite the Sun) this month at 8:01 a.m. Eastern Daylight Time (12:01 Universal Time), after the Moon has set as seen from the United States East Coast.
This means that observers in the Americas will see nearly full Moons on two successive nights — Aug. 21-22 and Aug. 22-23 — with the Moon appearing closest to full before dawn and again after dusk on the 22nd.
Historically, the term ‘Blue Moon’ was more often not an astronomical term: In older songs, it was a symbol of sadness or loneliness, while the phrase “once in a blue Moon” means a rare event.
However, in modern usage, the term has come to refer to the second full moon in a month (the last of these occurred on Oct. 31, 2020) — but that has not always been the case. It is actually a calendar goof that worked its way into the pages of an American astronomy magazine in March 1946 and spread around the world from there.
Editors and contributors have traced the traditional astronomical definition to the Maine Farmers’ Almanac in the late 1930s. The Almanac consistently used the term to refer to the third full Moon in a season containing four (rather than the usual three).
“Introducing the ‘Blue’ Moon meant that the traditional full Moon names, such as the Wolf Moon and Harvest Moon, stayed in synch with their season,” said Diana Hannikainen an editor for the American magazine.
But in 1946, amateur astronomer and frequent contributor to the periodical James Hugh Pruett (1886-1955) incorrectly interpreted the Almanac’s description, and the second-full-Moon-in-a-month usage was born.
The monthly magazine admitted to its ‘Blue Moon blooper’ in the March 1999 issue (“What Is a Blue Moon in Astronomy?”).
Canadian folklorist Philip Hiscock and Texas astronomer-historian Donald W. Olson worked with the magazine’s editors at the time to figure out the origin of the mistake, and how the two-full-Moons-in-a-month meaning spread into the English language.
By either definition, Blue Moons are still relatively rare. They happen about once every 2.7 years on average.
Only exceedingly rarely does the Moon actually turn blue in the sky, mostly when either volcanic eruptions or forest fires send lots of smoke and fine dust into the atmosphere.
Popular culture has also enthusiastically adopted the phrase “Blue Moon” and applied it to many different things.
(With inputs from ANI)
Edited by Amrita Das and Krishna Kakani
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