Rare Halloween blue moon will be visible for first time in 76 years

Last blue moon occurred in March 2018

A full moon glows at dusk in a cloud-filled sky. (Photo by Robert Alexander/Getty Images) (Robert Alexander, Robert Alexander)

Can we agree there are few things that sound creepier than a full moon on Halloween? Of course, we mean “good” creepy.

This year, a blue moon will fall on Halloween -- and it’s the first blue moon we’ll experience since the last one on March 31, 2018. Better yet, it’s the first visible one here in the United States for the first time in 76 years.

A blue moon, in case you’re wondering, isn’t blue in color at all — unless you’re talking about the other blue moon, which we’ll fill you in on shortly. A blue moon, by the most popular definition, according to meteorologist Paul Gross, is when two full moons appear in a single month.

“We will have full moons on Oct. 1 and 31, so that means that we’ll have a blue moon on Halloween,” Gross said.

This year, a Harvest moon crossed the sky on Oct 1. It refers to the full, bright moon that occurs closest to the start of autumn. The full moon to follow on the last day of the month then becomes a Halloween blue moon.

There were some people in the Central and Pacific time zones who got to trick-or-treat by the light of a full moon in 2001, but a true Halloween full moon hasn’t been visible for people in ALL time zones since 1944, according to Farmers Almanac. Even when a moon isn’t technically considered full, it may still appear full to the naked eye, so there’s a good chance you’ve seen a moon that’s about 98% full on some trick-or-treating nights.

Astronomers predict after this year, we won’t see a 100%-illuminated Halloween full moon until 2039. Following that, they say we’ll see it in the years 2058, 2077 and 2096.

The other full moon we mentioned earlier, which would be incredibly rare to see on Halloween, refers to when there are vast forest fires or major volcanic eruptions that cause the moon to take on a bluish or lavender hue, after soot and ash particles are propelled high into the Earth’s atmosphere.

Or maybe even a Supermoon, which can appear 14% to 30% brighter than a normal full moon, would really make the holiday.

Either way, this Halloween’s moon will be a rare occurrence, so make sure, despite your plans, you take a peek.