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A rare blue moon lights up the sky on Halloween

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(CNN) – Spooky season is almost here – and this year it will be a little more spooky.

The night sky on Halloween is lit up by a blue moon, the second full moon in a month. The relatively rare event occurs once every two and a half years, according to NASA’s National Space Science Data Center.

Every month has a full moon, but since the lunar cycle and the calendar year are not perfectly synchronized, approximately every three years, we end with two in the same calendar month.

The first full moon of October, also known as the harvest moon, appears on the first day of the month. The second full moon, or blue moon, will be visible on October 31

. It is the first occurrence of a blue moon in America since March 2018.

It is also the first time a Halloween full moon has appeared for all time zones since 1944, according to Farmers’ Almanac. The last time a Halloween full moon appeared was for the time zones of the Central and Pacific areas in 2001.

The “once in a blue moon” phenomenon does not necessarily mean that the moon looks blue on Halloween. While the dark blue tone of an evening sky can affect the color we see, the Earth’s satellite is unlikely to appear blue at all.

Normally when a moon takes on a bluish hue, it is due to smoke or dust particles in the atmosphere, for example during a major volcanic eruption.

When the phrase “once in a blue moon” was coined, it meant something so rare that you would be lucky (or unlucky) to see during your lifetime, according to NASA.

So if something unusual happens to you on Halloween, it may just be a good reason why.

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