Rare Blue Moon, the last until 2023, wows stargazers (photos)

A rare seasonal "Blue Moon" wowed skywatchers Sunday (Aug. 22), marking the last time this type of moon will grace the sky until 2023.

The full moon, also known as the "Sturgeon Moon," was not called blue for its color. Rather, it has to do with a scheduling rule that happens during a calendar year with 13 full moons, instead of the usual 12. 

If four full moons fall during one season, that's called a Blue Moon. A newer definition also defines a Blue Moon as the second full moon in a month, but that definition did not apply to Sunday's sky show.

Regardless of its name, the moon wowed skywatchers on multiple continents, as an informal survey of Twitter shows below.

Related: The August 2021 full moon is a Blue Moon. Here's why.

It will be two more years before another Blue Moon comes around, although again that depends on what definition you prefer to use.

If you use the "two full moons in a month rule", according to skywatching columnist Joe Rao, the next blue moon will also come in the month of August — Aug. 30, 2023 to be exact. 

But if you prefer the other definition saying the Blue Moon is the fourth full moon in a single season, that won't happen again until another August: Aug. 19, 2024.

Happily, the next full moon will happen a lot sooner than that. The Corn Moon is expected to reach its peak on Sept. 20, with other full moons in 2021 occuring on Nov. 19 and Dec. 18.

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Elizabeth Howell
Staff Writer, Spaceflight

Elizabeth Howell (she/her), Ph.D., is a staff writer in the spaceflight channel since 2022 covering diversity, education and gaming as well. She was contributing writer for Space.com for 10 years before joining full-time. Elizabeth's reporting includes multiple exclusives with the White House and Office of the Vice-President of the United States, an exclusive conversation with aspiring space tourist (and NSYNC bassist) Lance Bass, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, flying parabolic, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, "Why Am I Taller?", is co-written with astronaut Dave Williams. Elizabeth holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, a Bachelor of Journalism from Canada's Carleton University and a Bachelor of History from Canada's Athabasca University. Elizabeth is also a post-secondary instructor in communications and science at several institutions since 2015; her experience includes developing and teaching an astronomy course at Canada's Algonquin College (with Indigenous content as well) to more than 1,000 students since 2020. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday. Mastodon: https://qoto.org/@howellspace