"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."

Not all that rare

[PlazMatiC]

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

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.

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.

Black Moon is even more rare

[cyber_rigger]

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

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).

Ske & Telescope had an article about this...

[MaxRahder]

See the Sky & Telescope article: "What's a Blue Moon? The trendy definition of "blue Moon" as the second full Moon in a month is a mistake." http://skyandtelescope.com/observing/objects/moon/ article_127_1.asp

Re:Rare?

[Anonymous Coward]

But calling two full moons in one month a 'blue moon' first happened in about the 1920s when the Farmer's Almanac gave each full moon of the year a special name. The event of a double full moon was called a blue moon. Later (around 1985) Trival pursuit made it this into a question and this usage became popular.

picture of actual BLUE moon

[Anonymous Coward]

On APOD there a picture [nasa.gov] of a moon that's really blue.

Sig.

[Anonymous Coward]

Hey man, you do know that starcraft/brood war has been working under wine for a very long time?

link to transgaming [transgaming.com]. This game will also work under wine (I've gotten it working personally), cedega makes things sooo much easier. It's not perfect; battle.net has font issues, but apparently it's not a big deal if you've played battle.net before.

Note that transgaming says that brood war doesn't work, but it does; their game listing is not updated. I just recently installed brood wars in cedega 4 (formerly known as winex)

Re:Not all that rare

[Orinthe]

I don't know where this google calculator gets its numbers from, but blue moons are actually twice as common as it implies.

There are approximately 13 lunar cycles in a year, and 12 months. Simple math should be able to tell you that there must be a blue moon on average at least once a year--rarely two, and rarely none. In fact, over the next 20 years, 17 will have blue moons [infoplease.com].

That's about every 1.2 years.

Re:Rare?

[Nefarious Wheel]

And of course, in very old trade calendars (1930's or thereabouts IIRC) phases of the moon were prominently displayed with the calendar dates. If a page spilled over to another month, and a full moon was shown, it was invariably printed in blue ink.