"Blue Moon" Appears in Sky Saturday Night

ArbiterOne writes "Tonight a rare spectacle can be seen: the second full moon in a month, which is sometimes called the "blue moon", according to CNN. Don't be disappointed if it isn't actually blue, though; the blueness is caused by increased density of smoke or ash in the air, such as after a volcanic eruption."

Comments

Not all that rare

[PlazMatiC]

It's not that much of a rare occurrance .. Once every 2.7 years, even.

Re:Not all that rare

[swimboy]

The moon's cycle is about 29.5 days, which makes about 12.4 full moons a year. That means a blue moon about every 3 years.

The 17 blue moons in 20 years is due to two different definitions of what constitutes a blue moon. So, blue moons are twice as common, because there are two different ways to define what a blue moon is!

Re:Not all that rare

[Peter_JS_Blue]

Oh shit !! My friends say I only buy a round of drinks every blue moon - its going to be a very expensive night in my local pub this evening.

ARgh!

[mfh]

Now I have to do all that stuff I told everyone I would only do when the moon turns blue. *sigh*

Rare?

[MaelstromX]

From TFA:

The phrase "Once in a blue moon" was first noted in 1824 and refers to occurrences that are uncommon, perhaps even rare. Yet, to have two full Moons in the same month is not as uncommon as one might think. In fact, it occurs, on average, about every 32 months. And in the year 1999 it actually occurred twice in three months.

Re:Rare?

[severoon]

I heard that the adoption of the term blue moon in modern usage actually stems from a misappropriation of the term from some Native American tribe (around the time frame you mention, early 19th C). The term, as far as my uninformed and caffeine-addled mind can conjure at the moment, originally referred to an occurrence of a particular full moon that occurred during the three-month harvest season; specifically, when four moons occurred during this three month season, the third of the sequence was called a "blue moon". (The Wikipedia entry seems to make reference to this--see the second entry--but I can't find anything specific on it. Also, it doesn't seem to mention the "harvest" season, just any season, which is not what I heard from my unreliable source.)

This is why our concept of blue moon as the second in a month doesn't seem to make sense in terms of rarity...it's not that rare. It makes a bit more sense if we consider how often four moons occur during the three month harvest season. That was probably quite a bit more rare.

Re:Rare?

[drang]

(treating the months as independent of each other which obviously isn't the case but shouldn't affect the outcome)

It is not the case, it should affect the outcome, and it does. Using your figures and ignoring fractional days of a lunation, the day of the month on which a full moon occurs regresses 1-3 days each month, so if a "blue" moon occurs this month (in days 29-31) one can't occur next month (in days 26-28).

Re:Rare?

[SoSueMe]

Here is a really good explanation of the background on our current definition of a "Blue Moon" which seems to have been popularized by none other than Trivial Persuit.

On July 31 of this year, those taking an evening stroll beneath a cloudless sky will have the opportunity to look up and see what modern folklore refers to as a "blue moon." Though the moon itself will not actually be blue--or likely even appear blue--it will be the second full moon in the same calendar month of July, which is what qualifies this Saturday's lunar view as a blue moon, at least by today's standards.

That's not to say that the moon has never appeared blue in color to the average, unaided, ground-bound observer. The moon can and has shone blue or even green in color whenever a sufficient quantity of micron-sized particulates is present in the atmosphere, usually after a volcanic eruption.

The micron-sized debris (specifically, any particles slightly larger than the wavelength of red light, about 0.7 microns) refracts the moonlight, turning it green or blue, based on certain atmospheric factors. For an example of this phenomenon, one need look no further than accounts of blue moons following the eruption of the island of Krakatau in 1883.

While instances of actual blue-tinted moons represent one of several documented meanings of the term, using blue moon to describe the second full moon in one calendar month is a fairly recent practice. This definition arose in the 20th century, and it didn't really become part of the widespread public consciousness until the 1980s.

We can attribute this sudden proliferation of a previously undocumented and unused definition for blue moon to three otherwise reputable sources of fine information and fun trivia, all of which were working off bad information.

WHAT THREE MASS-MEDIA TRIVIA SOURCES ARE MOST RESPONSIBLE FOR THE NEWEST DEFINITION OF A "BLUE MOON"?

What three reputable mass-media trivia resources are most responsible for the current popular definition of a "blue moon" to mean the second full moon in the same calendar month, and what is the likely origin of this "mistaken" definition?

The most recent and most widely known source of the "new" blue moon definition is none other than the king daddy of all trivia board games, Trivial Pursuit. Specifically, the Trivial Pursuit Genus II edition published in 1986 included this definition as a question in the Science and Nature category.

Given the popularity of the game, it's little wonder that folklorists witnessed this definition enter widespread usage in the 1980s. But where did the game makers get their information?

Trivial Pursuit archives (yes, they exist) cite The Kids' World Almanac of Records and Facts, published in 1985, as the source of the question. The book's authors, however, can't trace their own source for this "fact."

So where did the Almanac authors get it? Folklorist Philip Hiscock suggests it came from our second mass-media source.

In January 1980, the National Public Radio (NPR) program "Star Date" featured a piece by Deborah Byrd that noted the "second full moon in one calendar month" definition of blue moon. Byrd cited a 1946 article in Sky & Telescope magazine as her source. Hiscock considers the "Star Date" broadcast as the likely source of the Almanac entry, and thus NPR is the second mass-media source to get blue moon "wrong."

The third, obviously, is the usually reliable Sky & Telescope magazine. A March 1946 article by amateur astronomer James Hugh Pruett titled "Once in a Blue Moon" contains the modern definition of the term, but it cites the 1937 Maine Farmers' Almanac as its source. No edition of that Almanac, however, contains the modern definition of a blue moon.

Several editions of the Almanac do list a different definition of a blue moon--the third, extra full moon of an agricultural season. The Maine Farmers' Almanacs of tha

Re:Rare?

[srleffler]

Sky and Telescope has published an article more recently, explaining what happened and their role in it. It is available online.

Once in a Blue Moon

[pipingguy]

Neat! Maybe that means my askslashdot submission will be accepted!

Rare?

[Finuvir]

We see a full moon every 28 days. So a month with 31 days will have a blue moon if it has a full moon in the first three days. The chance of that is 3/28. The chance of a blue moon in a 30-day month is 2/28. There are 7 31-day months, 4 30-day months. So chance of no blue moon in a year (treating the months as independent of each other which obviously isn't the case but shouldn't affect the outcome) is (25/28)^7 * (26/28)^4 which is about 43.4%. So there's a 56.6% chance of a blue moon in any year.

Very very rare

[Anonymous Coward]

It occurs slightly less often than IE is patched.

How rare?

[lildogie]

"A rare spectacle" that happens more often than U.S. Presidential elections. I guess that makes the elections a rarer spectacle.

interesting article about it in sky & telescop

[laejoh]

see article

From the article:

According to Canadian folklorist Philip Hiscock, the term "blue Moon" has been around for more than 400 years, but its modern calendrical meaning has become widespread only in the last 25. And as discovered five years ago, it can be traced to a mistake published in Sky & Telescope in the 1940s!

Black Moon is even more rare

[cyber_rigger]

When no full moons occur in a month (usually February).

Re:Black Moon is even more rare

[gnu-generation-one]

"Black Moon is even more rare: When no full moons occur in a month (usually February)"

That would make it 2018 then?

Blue moon: 31/Jan/2008, 9am
Worm moon: 01/Mar/2008, 10pm

b.t.w. I don't think it's "usually february", I think it is always february. Every month other than february is guaranteed to be longer than the synodic period (about 29.5 days), so is guaranteed to contain a full moon. (apart from the month in which you change from julian to gregorian calendars...)

I swear I'm not making this up

[TrickFred]

...I read the article, and casually mentioned to the wife that tonight was a blue moon. She looked at me, and said with a straight face, "So, does that mean we have to have sex tonight?"

Re:I swear I'm not making this up

[OldManAndTheC]

That reminds me, in a roundabout way, of one of my favorite jokes. A college psychology professor decides to quiz his students on their sexual habits. He asks the class how many have had sex more than once in the past week? Several raise their hands. How about once in the past week? More hands go up. Once in the past two weeks? And so on ... after he has gotten to once every two months, he notices that everyone in the classroom has raised his or her hand, except for one guy sitting in the back. So he goes on:

"Three months". Nothing.

"Four months". Nope.

"Six months". Still nothing.

"One year?!".

Finally the guy in the back practically leaps out of his chair, raising his hand up high and bouncing up and down enthusiatically. The prof acknowledges him, and asks, "Well if you only get it once a year, why are you so happy?". The geeky guy smiles and says:

"'Cause tonight's the night!!"

P.S. If your wife wears glasses, may I recommend blue filters? :)

Re:I wonder how it affects global tides?

[Neophytus]

None: The earth doesn't rely on a calendar so no pattern is changing.

So what?

[codexus]

This is just a calendar coincidence not any kind of astronomical event. And in fact it happens quite often. So really, there is nothing special to see here. Was that really worth mentioning on slashdot?

Woohoo

[SlightOverdose]

I'm gonna get laid!