The last blue moon of this decade will rise into the sky Saturday night, not to be seen again until 2021. Here’s everything you need to know about the exciting celestial event.

What is it?

A ‘Blue Moon’ is, essentially, the second full moon in one calendar month, or as the Old Farmer’s Almanac explains, it can also refer to the penultimate full moon in a season that has four.

Tonight’s full moon will be the third of four this spring.

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Why is this one special?

Despite the phrase ‘once in a blue moon,’ the phenomenon is not particularly rare (and not especially blue), occurring about once every two to three years. However, what’s curious about this one is that it’s going to be the last until August 22, 2021, making it the final blue moon of the decade.

When can I see it?

The visibility of any moon obviously depends greatly on local weather conditions, but in theory you should be able to gaze upon it from anytime late Saturday evening into the early hours of Sunday.

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