Pictures of the blue moon Friday have begun to go viral on Twitter as tweeters from all over post their own photographs. Most people know that the term "blue moon" doesn't mean that the moon is actually blue. However, some denizens of the Twitterverse have chosen to alter their images of Earth's only moon.

A blue moon occurs when there are two full moons in one month, and it typically happens roughly every two-and-one-half years.

The term "once in a blue moon" was popularized in 1946 when an amateur astronomer named James Hugh Pruett wrote about two full moons happening in one month for Sky & Telescope magazine. Inside the magazine, he said the now-famous rare happening only occurred "once in a blue moon," NBC News reported.

But the proverbial term "once in a blue moon" has been taken way out of context in this case. Generally, the term refers to something that rarely happens, and it is sometimes even a figurative way to say "once in a lifetime." However, blue moons actually occur, on average, every 2.7 years.

Astrophysicist Neil deGrasse Tyson tweeted about the issue a few days before the blue moon this weekend: "A month's second full moon is the blue moon. Not rare. More frequent than presidential elections, yet nobody calls them rare."

Regardless, it hasn't stopped the anticipation or excitement of the blue moon on Friday. It could be because it's the last blue moon people will see until July 31, 2015, NBC News speculated.

Friday's blue moon is exponentially more special than any other previous blue moon, though. It pays tribute to the world's first man to walk on the moon, Neil Armstrong, who died last week.

Armstrong's family wants everyone to see tonight's blue moon as a tribute to their beloved family member.

"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," the family said in a statement following his passing.

Click "Start" to see the Blue Moon slideshow.

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