Getty Images Full blue moon

This Friday, Aug. 31, might not be all that much fun for you, especially if you’re someone who vows to only do obligatory tasks once in a blue moon. Then again, if you’re a believer that good luck comes your way only once in a blue moon, Friday might be just the day you’ve been waiting for.

The fact is, for the first time since March 2010, we’ll gaze upon a blue moon this Friday, illustrating just how long that fabled stretch of time really is: almost 30 months. After Friday, you’ll have to wait another 36 months — until July 2015 — for the next one. So, it’s time to loosen up Friday and do all those things you say you do “once in a blue moon.”

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It’s a rare cosmic rising that will be unveiled, coincidentally, on the same day as astronaut Neil Armstrong’s funeral service. Armstrong, who died last Saturday at the age of 82, brought the fabled moon into mankind’s domain when he became the first man to walk on its surface in 1969.

Despite the colorful turn of phrase, you might be disappointed if you look into the sky. There will be no magical chameleon act performed by the moon on Friday. That’s because the phrase blue moon — dating back centuries with no pinpointed origin — is nothing to do with hue, but instead signifies a full moon happening for a second time in the same month. Full moons occur every 29 days. With a full moon having already appeared this month on Aug. 2, Friday’s full moon will turn blue, well, in name only.

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At times moons have actually appeared blue, but that phenomenon has nothing to do with full moons and everything to do with ash particles floating in the atmosphere. Varying volcanic eruptions over the last few centuries have sent up ash clouds. When the ash particles reach a certain width, they can block reds and yellow from getting to our eyes, giving us tints of blue — and sometimes green — moons.

Of course, we can’t rule out a volcano erupting between now and Friday evening, giving us an actual blue moon. But, then again, that only happens once in a blue moon.

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