A blue moon that looks blue, but the term has nothing to do with the colour (see history of the term below)
We’re in for an unusual event on December 31st, 2009, with the decade to be ending in a blue moon, which is the second full moon in the same month.
History of the term “blue moon” (Daily Mail UK)
The term ‘Blue Moon’ is steeped in British folklore. In Shakespeare’s day, Blue Moon simply meant rare or absurd.
Folklore expert Philip Hiscock said: ‘The phrase ‘Blue Moon’ has been around for more than 400 years, and during that time its meaning has shifted.’
The modern definition sprang up in the 1940s. In those days, the Farmer’s Almanac of Maine offered a very convoluted definition of a Blue Moon that included factors such as ecclesiastical dates.
The Sky & Telescope published an article in 1946 to try and clear up the meaning. Author James Hugh Pruett interpreted the Almanac as a Blue Moon being the ‘second (full moon) in a month.’
That was not correct but could be understood and the modern Blue Moon was born.
Those living in the late 19th century literally saw a blue moon in the years following the eruption of the Indonesian volcano Krakatoa in 1883.
Plumes of ash had risen to the top of Earth’s atmosphere which strongly scattered red light, while allowing other colour wavelengths to pass through.
Why and when blue moons occur
A full moon occurs every 29.5 days, from which the term month comes. Because it is less than a full month, every 3 years or so, you get a blue moon occurrence. The misalignment between the monthly calendar and full moon cycle also results in the solar calendar year, or Julian calendar year (after Julius Caesar), or the year as we in the Western world know it, that is 11 days longer than the lunar calendar year used by some Asian cultures. Chinese or Asian New Year celebrations are determined by this lunar calendar.
As for a blue moon ending the year, the previous one occurred in 1990, with the next one not coming until 2028, or 19 years in between. That means 190 years until the next blue moon ends a decade so if you do the math, that’ll be 2199.
Oooh! A blue moon to end a century! Now there’s something to live for… if only it would look anything different than a full moon. It’d be a long lifespan, but between now and then, medicine might allow us to live that long… if we don’t kill ourselves off first!
But let’s not get down here. It is a new year and decade coming after all. All the best to everyone!