Saturday, January 25, 2014

What is a blue moon?

  • Definition 1: The currently accepted meaning is that a blue moon is the second full moon in a single month which has two full moons. Usually a month has one full moon, 12 in total for a year. Every two or three years there are 13 full moons in a year.
  • Definition 2: Said to be the original meaning, a Farmers’ Almanac blue moon is the third full moon of a season (three months) that has four moons instead of three.
  • It takes 354.37 days for the moon to go around the earth 12 times, a lunar year. This does not match the same time it takes for the earth to go around the sun of 365.24 days, an earth year. This means very few years there is an extra moon that makes up this difference.
  • It is a common myth that a blue moon is called blue because of its colour – though the moon can turn a blue colour with certain volcanic ash in the air – which happens very rarely – perhaps, once in a blue moon, you would say?? The moon is more likely to turn red than blue with dust/ash particals in the air.
  • Blue moons can have a different occurrence on each side of the international date line. For example, the USA had one blue moon in 2009 (Dec 31) and Australia did not have any. But in 2010 Australia has two blue moons (Jan 31 and Mar 31) while the USA has none. This is because the USA is a day behind Australia and so a full moon in the last day of a month in the USA is a full moon on the first day of the next month in Australia and New Zealand. 
  • It is possible to have a year which has two months with a blue moon, and with that, another month that has no full moon. There are only ever a maximum of 13 moons in a year and a minimum of 12.
  • A year with no blue moons is called a 'metonic' year.

What is a black moon?

  • A black moon is a little used term - so much so that it's hard to find a definitive definition. However it is most likely the second new moon in a month (opposite of a blue moon). 
  • The other possible definition is the absence of a full moon (OR new moon) in a single calendar month - which can only happen in February.This is because it is the only month which has less days than a lunar cycle, meaning if there is a full, or new, moon a day before February then it won't be back until February finishes. If February misses a full or new moon then it means two other months will each have two full or new moons. February will always have either one full moon or new moon - it will never be missing both

What is a Wet moon?

What is a Dry moon?
What is a Cheshire Moon?

  • A wet and dry moon are both crescent moons but with different angles to the horizon.
  • The crescent moon in the summer time appears on an angle to the horizon, like a backward C, that you can picture it not being able to hold water, or if it was holding water previously, it is now pouring it out.
  • In winter the moon is a more parallel with the horizon, like a U, and you can picture it being able to fill up with water. The moon Winter moon is also called a Cheshire moon – because it looks like Alice in Wonderland’s Cheshire cat’s smile.
  • There is some confusion over which way around the definition or a wet and dry moon should be.
  • The reason for the changing angle of the crescent moon is because the Earth changes its tilt relative to the plane in which the moon orbits.
  • The path and angle of the moon is flipped left to right in the Southern Hemisphere compared to what the Northern Hemisphere sees.
  • Wet and dry moons have nothing to do with actual water on the moon or the moon causing any wet effects on earth

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