The term "blue moon" refers to the extra moon that falls in a month that has two full moons. Each 2.7 years there is a month that has two moons in it and this rare event (actually the first moon in this month) is referred to as a "blue moon." The phrase, "once in a blue moon" means something is rare.
The moon orbits the earth every 27.3 days, or roughly 13 times a year. This means that once (sometimes twice) per year the full moon will make its appearance twice in the same month. This second full moon is referred to as a "blue" moon.
Hence the expression, "once in a blue moon."
Over the next twenty years there will be a total of 17 blue moons, with an almost equal number of both types of blue moons occurring. No blue moon of any kind will occur in the years 2006, 2011, 2014, and 2017. The more recent phenomenon, where the blue moon is considered to be the second full moon in a calendar month, last occurred on July 31, 2004. Two full moons in one month may occur in any month out of the year except for February, which is shorter than the lunar cycle. The other, older blue moon event, which happens when there are four full moons in a season, last occured in August 2005. Since this type of blue moon is reckoned according to the seasons, it can only occur in February, May, August, or November, about a month before the equinox or the solstice.
See related question for when the next blue moon will occur.
A full moon is the phase that appears when the Moon is more-or-less "behind" the Earth in relation to the Sun. The Moon is on the direct line from the Sun to the Earth, and on the opposite side of the planet from the Sun. This reveals the maximum illumination of the lunar surface during its orbit of the Earth.
Note: Although the same side of the Moon always faces the Earth, the maximum area visible can change, due to a process called libration, so that more than 50% of the Moon's surface (about 59%) will be visible from the Earth at one time or another. The other 41% will never be visible from earth, although it receives the same average illumination from the Sun during its orbit. So photos of a full moon taken at one point during the year will be slightly different (around the edges) than at other parts of the year.
The phrase "blue moon," as in "once in a blue moon", doesn't refer to the moon being
actually blue. The modern usage defines it as the term used to describe the second full
moon to fall within the same calendar month. (This isn't common, but does occasionally
happen. Full moons are 29.5 days apart and there are never more than 31 days in a
month; so in order to have two full moons in the same month, the first one must occur
within the first 11/2 days of the month ... or even sooner if the month has only 30 days
in it.)
This definition only came about relatively recently (less than a century ago). Before
that, it was the third full moon in a season that had four. This happens every two or
three years (specifically, it happens 7 times in 19 years... the 19 year period is called
the "Metonic cycle" and by coincidence happens to be an almost exact multiple of both
the period of the lunar cycle (235 synodic months) and the solar cycle (19 tropical
years), only being off by a few hours).
Occasionally, the moon really does appear bluish. This is usually due to fine particulate
matter (aka "dust") in the upper atmosphere, and is basically the same thing that makes
distant mountains appear to have a bluish (or purple, as in "purple mountains' majesty")
tint at times.
"Once In a Blue Moon" is a popular expression meaning "very rarely." The Moon does not actually turn blue.
The expression comes from a very rare phenomena where we have two full moons in the same month. It only happens "once in a blue moon".
A blue moon refers to an astronomical event, not the moon actually being blue.
A blue moon is when there are 2 full moons in the same month. The full lunar cycle is 28 days long. So in some months there will actually be two nights with a full moon. This is referred to as a blue moon.
Alternately it can mean when there are 13 full moons in 1 year the last of the year being the blue moon.
A blue moon is when you have two full moons in one month. This is actually quite often - every 3 to 4 years.
As of Jan 2010:-
August 31st 2012 at 13:56 GMT
July 31st 2015 at 10:41 GMT
See link for calculator
Yes, because a blue moon is when there is a full moon twice in a calender month.
Once in a very long time or takes ages to happen A "blue moon" is when there is a full moon twice in a calendar month-which IS rare, but occurs, on average, every 2.5 years.
The moon is called a blue moon every 2.7 years because this is the only time in that period of years that there is a full moon twice in a month. There was one on the second of September and one today.
A blue moon appears once every two or three years. It is an astronomical phenomenon where the moon actually colors blue. This is why it is called a 'blue moon'.
Once in a blue moon! Well that is what the second full moon in a month is called, a blue moon. It is very irregular, sometimes it can happen multiple times a year or even two months in a row. Other times it can be years between them.
This is a blue moon. It happens very rarely, once every two to three years or so.
If they both are heterozygous and the recessive gene is blue it can happen
Once in a very long time or takes ages to happen A "blue moon" is when there is a full moon twice in a calendar month-which IS rare, but occurs, on average, every 2.5 years.
The moon is called a blue moon every 2.7 years because this is the only time in that period of years that there is a full moon twice in a month. There was one on the second of September and one today.
yes!
1 every 2-3 years
Blue whales can live to be as old as 40 years old. They are able to reproduce around 7 years old, and have a new offspring every few years.
A blue moon appears once every two or three years. It is an astronomical phenomenon where the moon actually colors blue. This is why it is called a 'blue moon'.
Months! A blue moon is when there are 2 full moons in 1 month.
A "blue moon" has been defined as two full moons in the same month. This can happen in any month except in February. It isn't all that rare; it happens about every other year.Two "blue moons" in the same year can only happen in January and March, which is what happens in 2018. That's because February is the only month in which it's possible to NOT have ANY full moons; February has only 28 days, and a month is 28.5 days!We can expect this (two "blue moons" in the same year) about every 31 years; any time the Moon is full on January 2, it will be full again on January 31, March 2 and March 31.
It didn't, we get one late next year, they don't happen every year
It only snows once in a blue moon. About once every few years.
Maybe. It's also possible that he actually has blue fur, which is likely since almost every animal in the series is an unusual color.