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.
Full Moon today (22nd August) 🌕🔭🔵Moonrise at Stonehenge is at 8.48pm, Moonset was at 5.26am #Sturgeon #BlueMoon #Fullmoon pic.twitter.com/CTeNlCdLEOAugust 22, 2021
Tonight’s rising #BlueMoon peeps through the clouds to briefly crown the UK’s tallest spire pic.twitter.com/nxnimUystlAugust 21, 2021
Tonight’s moon rising at Round Lake in the Ottawa Valley. #bluemoon pic.twitter.com/zH3URXTz5bAugust 23, 2021
Moonrise tonight 😍😍 I’m so excited to have the clear skies back 🔭✨🌙 #Moon #SturgeonMoon #BlueMoon #Cornwall #Clearskies #Luna #Astrophotography pic.twitter.com/nLFzeFwlvfAugust 22, 2021
Every once in a blue moon or so, I am able to film a #BlueMoon from the helicopter... as I did this evening over Los Angeles. Goodnight! @CBSLA #Sky2 #Sky9 #FullMoon pic.twitter.com/Uyq8kKSqqqAugust 23, 2021
August full moon and Jupiter in Los Angeles. #bluemoon 🌕 pic.twitter.com/A3AkqBzqxWAugust 22, 2021
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 firstname.lastname@example.org.
Follow Elizabeth Howell on Twitter @howellspace. Follow us on Twitter @Spacedotcom and on Facebook.