Armstrong was the first human being to set foot on the moon. He died last weekend at the age of 82.
Of course, the name "blue moon" is a little misleading: our moon won't be changing colour tonight. A blue moon is "the second full moon in a month with two of them," according to Space.com. According to folklore, the second moon in a month is "blue," which is where the name comes from.
It may not make all that much sense, but it definitely made for a great Elvis Presley performance (not to mention Billie Holiday and Mel Torme, who also covered it):
The phrase "once in a blue moon" usually refers to something really rare, but blue moons aren't that unusual - they take place an average of once every 2.7 years. Sometimes there are even two in one year (it happened in 1999).
Science@NASA has this video explaining where the name blue moon comes from, and the truly rare circumstances when a blue moon is actually blue:
While the moon will probably look as grey as usual this evening, it's kind of nice to think that our best-known satellite is feeling a little blue in sympathy for Neil Armstrong's family and friends.
In a statement released after his death, his family had a suggestion for people who want to pay tribute to him:
"For those who may ask what they can do to honour Neil, we have a simple request. Honour his example of service, accomplishment and modesty, and the next time you walk outside on a clear night and see the moon smiling down at you, think of Neil Armstrong and give him a wink."
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