Rare super blue moon coming to suburban skies Wednesday night

The phrase “once in a blue moon” refers to something that happens rarely — say a Chicago Bears Super Bowl victory, or a Chicagoan putting ketchup on a hot dog.

But astronomically speaking, blue moons aren't quite as rare as the idiom might have you believe. According to NASA, 3% of full moons qualify as blue moons. And you can see one in the night sky Wednesday.

Blue moon is the term for when we see the full moon twice in the same month, something that occurs every two to three years, NASA says. The next one after Wednesday will appear May 31, 2026.

Another definition comes from the 19th Century Maine Farmer's Almanac, which described a blue moon as the third full moon in a season that has four full moons. The next blue moon under that definition will appear Aug. 19, 2024.

What makes Wednesday night's noteworthy is that it also is a supermoon, which means that it coincides with the orbit of the moon making its closest approach to Earth. According to the website EarthSky, it will be the closest full supermoon of the year, with the moon about 18,000 miles closer to Earth than its average distance.

And that is rarer — you won't get another chance to see a super blue moon until Jan. 31, 2037. If you are around to see that, you also will be treated to a partial lunar eclipse.

As for Wednesday night's moon, observers may not notice much difference between it and a regular full moon, said Michelle Nichols, director of public observing at Chicago's Adler Planetarium.

“You won't notice a difference in size,” she said. “You might notice it looks a little brighter, maybe.”

If you are looking for the moon Wednesday — moonrise is at 7:42 p.m. Chicago time — you can spot it toward the southeast horizon.

“And it's not going to get very high above the horizon. So, if you've got a lot of trees and buildings in your specific vicinity, that may affect whether or not you may even see the moon at all,” Nichols said.

While the moon won't actually be blue in color, if certain atmospheric conditions exist — such as dust in the air or smoke particles from forest fires — they could create the appearance of a blue tint.

Nichols said Adler's observatory will be open Wednesday night, and the planetarium's Sky Observers Hangout show will broadcast on its YouTube channel beginning at 9 p.m.

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