(NEW YORK) — On Halloween, the sky will be lit up by a rare blue moon on the spookiest night of the year.

While it is called a blue moon, the moon won’t actually appear blue. The phrase refers to the time when a second full moon occurs in one month.

According to NASA, a blue moon occurs about seven times every 19 years.

This year, there will be a full moon on Oct. 1 and on Oct. 31.

The last blue moon appeared March 31, 2018, according to Earth Sky.

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