A rare Blue Blood Moon rises on Halloween. Here's what that means.

The full moon sets behind trees in the Taunus region near Frankfurt, Germany, Thursday, May 7, 2020. (AP Photo/Michael Probst)Michael Probst/AP Photo

• 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.

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

It's nothing to fear, though, despite the ominous name. A blue moon is the term for the second full moon in a single month, and a Blood Moon is simply the name for a full moon that falls in the month of October.

The backdrop is rare for October 31: Full-moon Halloweens only happen every 18 or 19 years, according to The Old Farmer's Almanac.

Across North America and Europe, people have used full moons to track months and seasons for thousands of years, naming each one based on the seasonal changes it indicates.

The names assigned to full moons are often attributed to the native Algonquian peoples, who share a family of languages and originate from the area that today ranges from New England as far west as Lake Superior. Colonial settlers across North America adopted their own version of the indigenous names, according to the Almanac.

Different languages and cultures characterized their moons differently, sometimes based on agricultural cycles, sometimes on natural phenomena. Here are some of the many names assigned to full moons throughout the year.