Photo from NASA, composite of 2 images sent back by Galileo.
From Denny: A second moon of the month will shine for New Years Eve, a rare event, so rare it won't happen again until 2028 on New Years Eve. The normal December moon is called by the Algonguin Native Americans a Cold Moon. Blue Moon generally refers to the 13th moon of the year. Second moons in a month happen from time to time but are rare on New Years Eve, the last day of the calendar year. Back twenty years ago in 1990, New Years Eve parties were themed around the "once in a Blue Moon"!
According to NASA: "Most months have only one full Moon. The 29.5-day cadence of the lunar cycle matches up almost perfectly with the 28- to 31-day length of calendar months. Indeed, the word "month" comes from "Moon." Occasionally, however, the one-to-one correspondence breaks down when two full Moons squeeze into a single month. Dec. 2009 is such a month. The first full Moon appeared on Dec. 2nd; the second, a "Blue Moon," will come on Dec. 31st. The modern astronomical Blue Moon occurs in some month every 2.5 years, on average. A Blue Moon falling precisely on Dec. 31st, however, is much more unusual."
HOW IT HAPPENS
While normally the moon is not blue there are conditions where it can appear blue to us on Earth. Back in 1883 when the Indonesian volcano Krakatoa erupted it put so much dust into the atmosphere that it turned sunsets green and the moon did appear to be blue all around the world and so the term "once in a blue moon" was invented. That blue moon effect from the erupted volcano lasted almost two years.
Another occurrence of a blue moon was in 1927 in India when a late monsoon created the perfect conditions for a blue moon. A blue moon was found in Newfoundland in 1951 when huge forest fires from Alberta, Canada littered the sky with copious amounts of dust particles.
MEANINGS OF THE PHRASE "ONCE IN A BLUE MOON"
There are six meanings that have evolved over about 400 years. Centuries ago, in Shakespeare era, the term "once in a blue moon" actually meant you were comparing something to be just as obviously absurd as a blue moon occurring. Eventually, it evolved into a second meaning that something would "never" happen. It's a lot like today when we say something will occur "when Hell freezes over" basically meaning that will never happen.
The main meaning of "once in a blue moon" came into our language when the volcano Krakatoa erupted creating the visual sight of a blue moon around the world for almost two years. It came to mean something that occurred infrequently and not quite regular enough to easily pinpoint.
There are six songs that include the blue moon reference as a symbol for sadness and loneliness. Half of the songs claim the lover's moon turned into gold when he achieved his love.
The most recent meaning in our time is that a blue moon is a second moon in the same month, which can occur at any time of the year. Technically, this perception is not accurate since the public judges this second moon by the calendar year.
The true blue moon comes from the tropical year - going from the Winter Solstice to the next instead of starting on 1 January and going to 31 December like the calendar year - where it is actually the third moon in a season with four, according to Sky and Telescope. You see the tropical year normally has 12 full moons, four for each season. Occasionally, there are 13 full moons so that one season has four full moons instead of usual obvious three.
CONCLUSION
Blue Moons happen about one for every 2.72 years in a century of 1200 calendar months and 1236.83 Full Moons. That averages out to about 3% of Full Moons are Blue Moons. So, enjoy this rarity on New Year's Eve!
BONUS: And if you live in Europe and Asia there will be visual - only to you - a partial lunar eclipse to send out the "00" decade for this century.
*** THANKS for visiting!
