A Rare Blue Blood Moon arises on Halloween. Here's what that means.

By: Rebecca Harrington, Morgan McFall-Johnsen writing for Business Insider
 

A Blue Blood Moon — the second full moon this October — rises in the night sky on Halloween. 

People across North America and Europe have used full moons to track the seasons and months for thousands of years.

Here are some of the names they've used for each month's full moon.

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A Blue Blood Moon will hang in the sky on Halloween.

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