The August 2021 full moon is, somehow, a Blue Moon. Here's why.

[Judi Lynn]

By Joe Rao - Skywatching columnist about 7 hours ago

It rises Aug. 22!

Next Sunday (Aug. 22) brings us the August full moon and in addition, it will also be a "Blue Moon."

But wait a minute, you might ask: Isn't a "Blue Moon" defined as the second full moon that occurs during a calendar month? The full moon on Aug. 22 is the only full moon this month. So, how can we call it a Blue Moon?

Yet it indeed is a Blue Moon — but only if we follow what is now a somewhat obscure rule. In fact, it was the original definition for branding a full moon as "blue."

The almanac rule
Back in the July 1943 issue of Sky & Telescope magazine, in a question and answer column, there was a reference made to the term "Blue Moon." The unusual term was cited from a copy of the 1937 edition of the now-defunct Maine Farmers' Almanac.

More:
https://www.space.com/blue-moon-2021-explained?utm_source=notification

[wendyb-NC]

1. Very interesting

The 1937 description, does make the 4 moons in a season rare or once in a blue moon. The 3rd moon of the season season chosen to be the blue one, to maintain the designation of a late or last moon of that season. Thank you for posting.