"Once In A Blue Moon..."

According to the old adage, if a situation or event seldom or rarely occurs, it is said to happen "once in a blue moon." But what is a 'blue moon' to begin with? At least in current usage, it refers to a second full moon within a given calendar month. At 9:04 PM EDT tomorrow, Thursday May 31, we'll have our second full moon this May, thus a 'blue moon'.

Is it really blue? No. Through recorded history there have been all sorts of moon colors reported (along with sun colors, sky colors, etc.) as a result of cataclysmic events such as large-scale volcanic eruptions (Krakatoa, Mount St, Helens, etc.), massive dust storms, or expansive fires...but tomorrow's blue moon will look like any other: gorgeous.

How rare are they? They're not. In fact, they happen more than you think. On average there is a blue moon every 32 months, but they happen irregularly, the best way to put it. In January and March of 1999, there were 2 blue moons in that 3-month stretch, which is more rare as that happens maybe 4 times a century.

Are there are any months where a blue moon has never been recorded? Since there is about a 29.5 day span between full moon phases, blue moons are impossible in February...in like thinking but flipping the coin over, February is also the only month that can have no full moon whatsoever.

With all that said, time to back up the bus...the above definition is actually a misinterpretation of the much earlier usage of the term 'blue moon' from the 19th century...before the mid part of the 20th century, a 'blue moon' was the third moon in a four-moon season, which normally would have 3 full moons. By that definition, statistical occurrences change, etc...one article I read put it in proper perspective, though, as people dickered over proper usage of the term:
the modern (mis)interpretation is like a genie that has gotten out of its bottle.

Marvel at the moonshadows, y'all!