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

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The sky show had nothing to do with color.

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The August Sturgeon full moon rises behind the Hortiatis mountain and Thessaloniki city in Greece, on Aug. 22, 2021.
The full moon rises behind the Hortiatis mountain and the city of Thessaloniki in Greece, on Aug. 22, 2021.(Image credit: Nicolas Economou/NurPhoto via Getty Images)

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.

Editor's note: If you have an amazing night sky photo or video that you'd like to share for a possible story or image gallery, please contact editor in chief Tariq Malik at spacephotos@space.com.

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Elizabeth Howell
Elizabeth Howell
Staff Writer, Spaceflight

Elizabeth Howell (she/her), Ph.D., is a staff writer in the spaceflight channel since 2022 specializing in Canadian space news. She was contributing writer for Space.com for 10 years before joining full-time. Elizabeth's reporting includes multiple exclusives with the White House, 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?" (ECW Press, 2022) is co-written with astronaut Dave Williams.