What exactly is meant by a blue moon?

Question

I have heard several contidictory answers.

Answer 1

The older meaning of blue moon to name an extra full moon, as was used in the Maine Farmer's Almanac, was the third full moon in a quarter of the year when there were four full moons – normally a quarter year has three full moons. The division of the year into quarters for this purpose has the dividing line set between March 21 and March 22. This has to do with the rule for setting the date for the Christian Holy Day of Easter, which depends on the last full moon - or before the Equinox on March 21, which is also somewhat inaccurate.
Calendar blue moons occur infrequently, and the saying once in a blue moon is used to describe a rare event. However, they are inevitable because of the mis-match between the solar and lunar cycles. Each calendar year contains twelve full lunar cycles, plus about eleven days to spare. The extra days accumulate, so that while most years contain twelve full moons to match the twelve months, every two or three years there is a year with thirteen full moons. On average, this happens once every 2.72 years. Additionally, in some years there is no full moon in February at all, since February is slightly shorter than the time from one full moon to the next. This condition, known as black moon, gives additional 'blue' moons in the preceding and following months (namely January and March). The last time this occurred was in 1999, and the next occurrence will be in 2018, according to UTC.
A blue moon occurs approximately 41 times in a century--giving meaning to the phrase, "once in a blue moon", to mean a rare occurance.
Also, the appearance of a blue moon in a quarter has to do with the different time zones.
Blue moons have been associated with superstition in the past. It has been said that the face of the moon talks to people when it is blue. It was called a blue moon, not because of the color of it, but because that was the folklore name for it, like the harvest moon, the blood moon, etc.

Thanks, I learned a lot. I knew what it was (and I suspect you did also) but did not know how it was figured.

Answer 2

Scientifically, the term "blue moon" is the second full moon in a month. Usually, only one full moon appears per month, but the occurrence of a blue moon happens once every 15 months. The first full moon would happen on the 1st of that month, and the blue moon, or second full moon of that month, would happen on the 30th.

Literally, an observer on Earth can see a blue moon in the sky, and the moon does not have to be full in order to be blue. The blue color is a result of chemicals and particles floating around in the air off of which light is refracted. The human eye sees the blue color. This happens often after forest fires.

As a phrase of speech, 'blue moon' was often used in the phrase 'once in a blue moon'. This had to do with something happening rarely or not due to happen for a very long time.

Answer 3

There are more than one meanings to a blue moon. The older, more recognized definition is then there is an extra full moon during a quarter of a year. When a quarter of a year sees a 4th full moon when there should be only three, the extra full moon is reffered to as a blue moon.

Answer 4

it IS the second full moon cycle in a calandar month.. It was also known as the lovers moon, Blue refering to the idea that during the first full moon of the month, people would fall in love, but the second one or both of the partners may fall inlove again... only maybe not with each other... so hence.. blue.

Answer 5

A blue moon is the second full moon in a month.

Answer 6

That's when you are seen standing alone, without a dream in you're heart, without a love of you're own.
No, that's Elvis' impression of Blue Moon. Sorry. All the above.

Answer 7

it has something to so with two full moons in one month