Blue Moon what is that means?

Tonight's blue moon may not be as rare as it sounds, but it's still special — as is every glorious full moon, whichever color you use to describe it.

Actually, the term "blue moon" is something of a misnomer. There's no reason for the full moon to be any bluer than usual (thoughit's certainly possible for the moon to take on a blue tinge). Instead, it has to do with the extra occurrence of a full moon in a given calendar cycle.

Various cultures have used different terms to describe that extra lunar cycle — Adhik Maas for Hindus, or an extra month of Adarfor the Jewish calendar. The Maine Farmers' Almanac used the term "blue moon" to describe an extra moon in a particular quarter of the year.

Then, in 1946, an amateur astronomer named James Hugh Pruett wrote about the phenomenon for Sky & Telescope magazine, in the context of the old saying that a rare occurrence happened only "once in a blue moon."

Only problem was, he got it wrong.

Pruett described the blue-moon phenomenon as the second full moon in a calendar month. Sky & Telescope stuck with that, and the definition has been used (and hotly debated) ever since. If you go along with the definition, then tonight's full moon is blue due to the fact that it follows a full moon on the night of Aug. 1.

There's another long-debated issue surrounding blue moons: You could argue that they happen way too often to be considered as rare as a "blue moon" in the proverbial sense. The interplay of the lunar and solar calendars dictates that a blue moon should occur, on average, every 2.7 years.

Astrophysicist Neil deGrasse Tyson summed up the issue a couple of days ago in a Twitter update: "A month's second full moon is the blue moon. Not rare. More frequent than presidential elections, yet nobody calls them rare."

Technically speaking, the moon is already a few hours past its full phase — but it's still well worth taking note of, and not just because it's the last blue moon until July 31, 2015. It provides a fitting opportunity to pay tribute to history's first moonwalker, Neil Armstrong, who passed away last weekend. In fact, Armstrong's family is urging you to look at the moon in Neil's honor.

"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.