A blue moon, the second full moon of a calendar month, rises on October 31, 2020 ( AFP / Emmanuel DUNAND)

There will not be a blue moon on Halloween 2021

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Facebook posts claim that a blue moon will appear on Halloween, October 31, 2021. Although this phenomenon did happen in 2020, it will not this year, according to the US space agency NASA and the Farmers' Almanac.

"There's going to be a full blue moon on 31 october 2021 that is halloween for the first time in 76 years," says an October 27, 2021 Facebook post.

Screenshot taken on October 27, 2021 of a Facebook post

Other examples of the inaccurate claim appeared on Instagram here and here.

However, a blue moon, or the second full moon to occur in a single calendar month, will not appear this Halloween. Neither will a seasonal blue moon, or the third full moon in a season that has four full moons.

A blue moon was visible the night of Halloween in 2020, but it is not an astrological event that occurs every year. On average there will be a blue moon every two and a half years, according to NASA

NASA offers a full moon guide that includes a tool allowing you to see the phases of the moon and the days on which they occur. It shows that on October 31, 2021 a waning crescent moon will be visible in the night sky.

Screenshot taken on October 28, 2021 of the NASA moon guide

The Farmers' Almanac calendar also shows that a full moon rose October 20, 2021 and that there is no secondary blue moon scheduled. This year did see a rare seasonal blue moon -- also known as a Sturgeon moon -- on August 20.

The next blue moon will not be until August 31, 2023, while the next seasonal blue moon will occur on August 19, 2024, according to the Almanac.

AFP has debunked other inaccurate claims regarding space and astrological events here.

October 29, 2021 This story was updated to fix a typo.