Blue Moon Tuesday, But Not the Kind You Think

Hey stargazers, get ready for a blue moon tonight — though it’s likely not the kind you’re thinking of.

First: No, the moon will not actually be blue. Second: This is not the second full moon in the month of August, the definition most people probably think of.

Instead, when Tuesday’s full moon rises to its peak at 9:45 p.m. eastern time, it’ll be a “seasonal blue moon” — the third of four full moons in a season. A seasonal blue moon hasn’t happened in nearly three years, EarthSky reports. 

LIVE: Watch the full moon rise tonight via weather.com

That we call two different events blue moons is a relatively recent error: In 1980, a radio program used as its source an inaccurate 1946 article from Sky & Telescope magazine. The third-full-moon-in-a-season definition is actually correct, but the modern version is “like a genie that can’t be forced back into its bottle,” the magazine wrote in 2006. 

(MORE: Highlights from the Perseid meteor shower) 

And while the celestial body itself won’t actually be a sapphire hue this time around, there can actually be a blue-colored moon, according to NASA’s Tony Phillips.

“There was a time, not long ago, when people saw blue moons almost every night. Full moons, half moons, crescent moons — they were all blue, except some nights when they were green,” Phillips wrote for NASA’s Solar System Exploration. “The year was 1883, the year an Indonesian volcano named Krakatoa exploded.”

The ash, he continued, caused the unlikely shades, with particles large enough to “strongly scatter red light, while allowing other colors to pass,” Phillips wrote. “White moonbeams shining through the clouds emerged blue and sometimes green.” Krakatoa’s not the only blue-moon causer. It happened afterMount St. Helens erupted in 1980, and again after Mount Pinatubo’s event in the Philippines 11 years later.

Rodgers and Hart immortalized the blue moon in their 1934 song by the same name, one that Elvis and Billie Holiday and Mel Tormé all covered. But it’s a good thing the moons described in songs aren’t all real; if they were we’d have to look far beyond a cobalt moon to a red one, a black one, even a chartreuse one. (NASA compiled a list of tunes that describe the rainbow colors of the moon; the titles clocked in at 19.)

Though blue moons happen more often than “once in a blue moon,” enjoy tonight; the next seasonal one isn’t until May 21, 2016.

MORE FROM WEATHER.COM: A supermoon! (PHOTOS) 

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The supermoon sets near the Statue of Liberty, Sunday, June 23, 2013, in New York. (AP Photo/Julio Cortez)