How rare is having two full moons in one month? *Cue “once in a blue moon” joke*

This year, we’re set to see two full moons in one month — twice. If you’ve ever watched a werewolf movie (Harry Potter and Twilight totally count), you know that the full moon is visible from planet Earth about once a month. And even though the Gregorian calendar — which is your average January through December calendar — evolved from the lunar calendar, the months of the year don’t quite align with the moon’s cycle.

Because of that, sometimes there will be two full moons in one month — and it’s happening twice in 2018. According to NASA via, there was a full moon on Jan. 1 and there will be another on Jan. 31. March will bring a similar fate, with full moons falling on March 1 and March 31.

The frequency of two full moons in one month simply depends on when the first one falls. If there is a full moon at the very beginning of a month, it’s likely there will be another before the month is out, since a full moon occurs roughly every month. The second full moon in a month is actually called a blue moon.

So how often do we experience two full moons in the same month?

Well, as noted by EarthSky, it typically happens every 2-3 years. 2018 must be special, because two blue moons are on the agenda. Ever wonder where the phrase “once in a blue moon” came from?

The second full moon in January will technically be a “super blue blood moon,” reports Business Insider. That means it will be a blood moon (a totally eclipsed moon that sometimes casts a red hue), a blue moon (the second full moon of the month), and a super moon (a full moon that appears extra large in the sky) all at once. And it will be the first super blue blood moon for the first time in over 150 years.

Not to mention, there are a ton of ways to use the phases of the moon for your benefit — so mark your calendars for Jan. 31!

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