Moon-gazers will get a treat this year because 13 full moons will occur including a rare blue moon on Halloween.

Now that's cool. And spooky.

A blue moon is the second full moon in a month and in October full moons will appear on Oct. 1 and Oct. 31.

Since an average lunar cycle is roughly 29½ days, two moons in the same month don't happen very often — usually every two to three years — hence the phrase "once in a blue moon." The extra moon in a month has been called a blue moon for many years, with the earliest recorded use of the term in English dating back to 1528.

The lunar cycle is also why there are never two moons in February, even in a leap year like this year.

The last blue moon happened in 2018, an unusual year for full moons since there were blue moons in both January and March. That year also had 13 full moons because there was none in February.

A full moon on Halloween happens roughly once every 19 years. The last Halloween with a full moon was in 2001. And for the nerds who are wondering — this century will get six Halloween full moons, with the next after this year happening in 2039.

Cue the wolf's howl.

This year we'll also get two supermoons when the moon will be full while it swings closest to Earth. Since the moon's orbit is an oval, Earth's celestial neighbor is sometimes far, with the farthest point called apogee, and sometimes near, called perigee.

Full moons on March 9 and April 7 will occur during the moon's perigee. Though it's usually difficult to tell a difference for folks simply craning their heads to look up at the sky, supermoons can appear as much as 14% larger and 30% brighter.

Friday night is the first full moon of 2020, known as the wolf moon. It becomes full at 1:21 p.m. but will look full for a couple nights.

It's called the wolf moon because wolves typically howl more during the breeding season in January and February. The January full moon is also known as ice moon, snow moon and moon after yule.

Folks in most of southern Wisconsin likely won't see the full moon, though, because snow and a wintry mix are forecast to fall throughout Friday and Saturday.

This month's full moon will also be special elsewhere on the globe because it coincides with a penumbral lunar eclipse, when the moon enters Earth's outer shadow but misses its darker inner shadow. The moon will appear darker, but the changes are subtle.

Here's a bummer — the wolf moon eclipse will be visible in Europe, Australia, Asia and Africa but not in Wisconsin.