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

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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)
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The full moon shines over the Church of St Catherine (left) and St Isaac's Cathedral in St. Petersburg, Russia, on Aug. 21, 2021.

The full moon shines over the Church of St. Catherine (left) and St Isaac's Cathedral in St. Petersburg, Russia, on Aug. 21, 2021. (Image credit: Peter Kovalev/TASS via Getty Images)
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The Sturgeon Moon appears over Idlib, Syria on Aug. 21, 2021.

The Full Sturgeon Moon appears over Idlib, Syria on Aug. 21, 2021. (Image credit: Muhammed Said/Anadolu Agency via Getty Images)
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The August Sturgeon full moon rises behind the Hortiatis mountain and Thessaloniki, 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)
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The full Sturgeon Blue Moon rises behind the torch of the Statue of Liberty in New York City on Aug. 22, 2021 as seen from Jersey City, New Jersey.

The full Sturgeon Blue Moon rises behind the torch of the Statue of Liberty in New York City on Aug. 22, 2021 as seen from Jersey City, New Jersey. (Image credit: Gary Hershorn/Getty Images)
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The full Sturgeon Blue Moon rises behind the torch of the Statue of Liberty in New York City on Aug. 22, 2021 as seen from Jersey City, New Jersey.

The full Sturgeon Blue Moon rises behind the torch of the Statue of Liberty in New York City on Aug. 22, 2021 as seen from Jersey City, New Jersey. (Image credit: Gary Hershorn/Getty Images)
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A 92% illuminated waxing gibbous moon rises above lower Manhattan and One World Trade Center ahead of the Full Sturgeon Moon and Blue Moon in New York City on Aug. 19, 2021 as seen from Jersey City, New Jersey.

A 92% illuminated waxing gibbous moon rises above lower Manhattan ahead of the Full Sturgeon Moon and Blue Moon in New York City on Aug. 19, 2021, as seen from Jersey City, New Jersey. (Image credit: Gary Hershorn/Getty Images)
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The full moon rises over the city of St Petersburg, Russia, on Aug. 21, 2021.

The full moon rises over the city of St Petersburg, Russia, on Aug. 21, 2021. (Image credit: Peter Kovalev/TASS via Getty Images)
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The Blue Moon is seen at the Independence Monument in São Paulo Brazil, on Aug. 22, 2021.

The Blue Moon is seen at the Independence Monument in São Paulo Brazil, on Aug. 22, 2021. (Image credit: Amauri Nehn/NurPhoto via Getty Images)
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The full moon shines over St. Isaac's Cathedral in St. Petersburg, Russia 21, on Aug. 21, 2021.

The full moon shines over St. Isaac's Cathedral in St. Petersburg, Russia 21, on Aug. 21, 2021. (Image credit: Valya Egorshin/NurPhoto via Getty Images)
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A plane flies past the full moon over Ankara, Turkey on Aug. 22, 2021.

A plane flies past the full moon over Ankara, Turkey on Aug. 22, 2021. (Image credit: Metin Aktas/Anadolu Agency via Getty Images)
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Jupiter and Saturn are seen as the full moon rises over a burning hillside in the Sequoia National Forest near Lake Isabella, in Kern County on Aug. 21, 2021 where the French Fire continues to burn in a heavily wooded area with 12,037 acres burnt and evacuation orders in place for nearby residents.

Jupiter and Saturn are seen as the full moon rises over a burning hillside in the Sequoia National Forest near Lake Isabella, in Kern County, on Aug. 21, 2021. (Image credit: Frederic J. Brown/AFP via Getty Images)
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The moon rises with Saturn and Jupiter on Aug. 21, 2021 in Korla, China.

The moon rises with Saturn and Jupiter on Aug. 21, 2021 in Korla, China. (Image credit: Xue Bing/VCG 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.

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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.

Follow Elizabeth Howell on Twitter @howellspace. Follow us on Twitter @Spacedotcom and on Facebook. 

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Elizabeth Howell

Elizabeth Howell is a contributing writer for Space.com who is one of the few Canadian journalists to report regularly on space exploration. She is the author or co-author of several books on space exploration. Elizabeth holds a Ph.D. from the University of North Dakota in Space Studies, and an M.Sc. from the same department. She also holds a bachelor of journalism degree from Carleton University in Canada, where she began her space-writing career in 2004. Besides writing, Elizabeth teaches communications at the university and community college level, and for government training schools. To see her latest projects, follow Elizabeth on Twitter at @howellspace.