A Rare Blue Moon Will Be Visible This Halloween

No, we’re not talking about the Colorado-based beer brand, we mean the rare occurrence where two full moons appear in the same calendar month. And the next blue moon just so happens to fall on this year’s Halloween.

This event has a pretty inaccurate name though, since the second moon isn’t actually blue, as awesome as that would be. To make things even more confusing, the moon can appear blue for completely unrelated reasons, such as atmospheric dust particles creating a color filter for the moon’s light. Still, no amount of strange naming decisions stops the actual blue moon from being a spooky oddity that will be perfect for the season.

This astrological surprise last occurred on March 31st, 2018 and is not projected to be seen again until August 22nd, 2021, according to earthsky.org. It seems that a blue moon really does only occur once in a… well, you get the idea.


The blue moon is only one of many reasons to look forward to this year’s Halloween, though. Many of the holiday’s enthusiasts have expressed excitement on social media at 2020’s event also featuring an extra hour at 2 A.M. due to daylight savings coinciding with the additional full moon. It also falls on a Saturday, giving adults more time to party and children more time to trick-or-treat without having to hear about school nights.

For more than half a century, whenever two full Moons appeared in a single month (which happens on average every 2 1/2 to 3 years), the second has been christened a “Blue Moon.” In our lexicon, we describe an unusual event as happening “Once in a Blue Moon.” This expression was first noted back in 1821 and refers to occurrences that are uncommon, though not truly rare.

When you look at the full Moon on Halloween night, it won’t appear blue in color but you’ll be looking at something pretty uncommon. A full Moon on Halloween only occurs roughly once every 19 years (known as a Metonic cycle). If the full Moons are calculated using Greenwich Mean Time, that translates to approximately 3-4 times per century. So maybe the phrase “once in a Blue Moon” really belongs to a full Moon on Halloween!

We’ll hopefully be able to spend Halloween watching the blue moon together with our friends.


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