A seasonal Blue Moon will appear in the skies tonight – the third full moon in the four-moon season between the June solstice and the September equinox.

The seasonal blue moon is different from the other rare lunar occurrence dubbed a Blue Moon – when there’s a second full moon in a single month. Though people are more familiar with the second full moon in a month definition of Blue Moon, the seasonal Blue Moon definition was actually the original.

Both Blue Moons, however, are equally as rare, notes Earth Sky. Therefore, the “once in a Blue Moon” idiom holds true no matter which one is being referenced.

“It’s inevitable that 7 out of 19 years will feature two full moons in one calendar month,” according to Earth Sky. “And it’s also inevitable that 7 out of 19 years will have four full moons in one season.”

The Blue Moon will rise tonight, Aug. 20, on the East Coast sometime after 7 p.m. and set around 7 a.m. on Wednesday morning. The third full moon of the season will be 100% full and glowing between 9:30 and 10 .m. ET.

Tonight’s full moon is also known as the Sturgeon Moon. It had received the nickname from Great Lakes fishing tribes that found that this particular moon appeared when they were able to catch the most sturgeon, according to the Old Farmer’s Almanac.

– Chelsea Regan

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