|We're used to seeing a full moon once every month but this December we're going to be treated to a 'once in a blue moon' event...|
Yes, this month we'll have *two* full moons - something that only happens every three years or so due to the difference between our calendar months and the lunar month.
The first of these was on 2 December 2009 and the second will be on New Year's Eve, 31 December 2009.
Throughout history different cultures have given names to the full moons that reflect, perhaps, events or festivals taking place around that time.
Not surprisingly, the Celtic tradition is to name it the Cold Moon in December.
In the more southerly half of the UK it is called the Oak Moon - perhaps a reference to the druidic practice of collecting mistletoe from Oak trees.
Whatever its history, this month's Blue Moon is something that won't be repeated until 2015.