A rare and magical event takes place this New Year's Eve - and I don't just mean the turning of the decade. When we are getting ready to say goodbye to the old year and usher in the new one, there is a Blue Moon - according to some people at least.
Many people say that whenever there is a second full moon in a single month, it is called a Blue Moon. According to the Blue Moon Calculator that next happens on December 31 2009 at at 7.11pm GMT.
But the definition of a Blue Moon is subject to argument and debate, although most people agree it is a full moon that does not follow the usual pattern of a single moon in each of the 12 months of the year.
Lunar months are 28 days, but calendar months are mostly longer, so there are about 11 extra days every year. This means that every two to three years there is an extra full moon. Different definitions place the odd moon out at different times.
Christians historically called the extra moon the "Betrayer Moon". Betrayer is "belewe" in Old English, which sounds a bit like the word blue. Mind you, in Norman French "bel ewe" means "beautiful water" and is the origin of the family name Bellew. I'm sure that double meaning could have caused some confusion in historical times.
According to Wikipedia, Christian clergy placed the so-called Betrayer Moon at Lent in years when the moon was extremely early in the season before Easter.
An American definition from the early 20th century defined a Blue Moon as an extra full moon that took place in a single season. A season normally has three full moons. If it had four, the third full moon was called a blue moon.
The common modern definition of a Blue Moon as being the second full moon in a month is wrong, according to The Farmer's Almanac. It says that this comes from a mistake first published in the March 1946 edition of Sky & Telescope magazine and that earlier definitions are more accurate.
In folklore, the full moon for each month has a different name. Although the names themselves vary from culture to culture, there are generally only 12 of them and they relate to things that are expected to be happening in nature or food production at that time. For example, December's full moon might be called "Snow Moon" or "Long Night Moon" while August or September's full moon might be called "Harvest Moon".
This meant that in years with 13 full moons, the first full moon of a month with two moons could be a bit early. Calling the first full moon in a month with two the blue moon instead put this useful device for seasonal calculations back on track.
The most literal meaning of a Blue Moon is when the moon looks blue from the Earth. This can be caused by pollution or smoke particles in the atmosphere. It doesn't have anything to do with the phase of the moon at all, but is rare.
Whatever your definition of a Blue Moon might be, this New Year's Eve will be a magical time with the full moon in the sky and everyone making their wishes for the future. If you do believe in the power of the Blue Moon, however, you might want to put on something blue to mark the occasion and call on the power of this rare event to make some seemingly out-of-reach dream come true.
The picture, entitled Blue Moon, comes from Enchanted: The Faery and Fantasy Art of Linda Ravenscroft available through Amazon
Enchanted: The Faery and Fantasy Art of Linda Ravenscroft