The full Blue Moon of 2010 occurs on November 21st at 10:29 a.m. Mountain Time. In recent years the popular definition of a Blue Moon is the second full moon occurring in a single calendar month. November only has one full moon this year, but it is still a Blue Moon.
The term “blue moon” has been around for many centuries and has multiple definitions. One of the earliest usages of the phrase began in the sixteenth century as a genteel idiom. “When the moon turns blue” was used then as we use the phrase “when hell freezes over” today. Both indicate a reference to an event that will never happen.
The moon has in fact appeared blue on several occasions; usually due to weather related events. One of the most phenomenal instances recorded is the eruption of the volcano Krakatoa in 1883. Dust and ash turned the moon blue for over a year.
The term blue moon became an official moon name when Gregorian monks realized that every now and then our twelve month year contained thirteen full moons. The cycle of the moon syncs up quite nicely with the Gregorian calendar. An average lunar cycle is approximately 29.5 days and an average month is around 30 days. This slots one full moon into each month. The four seasons which contain three months then have three full moons, one for each month. But, when a season contains four full moons, as it sometimes does, that extra moon causes problems for the organized calendar year.
Full moons were used by Gregorian monks to determine Christian moveable feast days. When confronted with this errant extra full moon, which interfered with the normal scheduling of holidays, churchmen of old singled it out and branded it a Blue Moon. The terminology was already in place for everyone to recognize this extra full moon as an unusual event
The third moon a season was chosen to be the Blue Moon. The fourth moon could then retain the original name of the last moon of that season. The practice of using the cycles of the moon to determine holidays is still used today. Easter is determined by the date of the full Paschal moon. All other feast days are based on this date.
This year, the November full moon is the third full moon of fall. The fourth full moon falls on December 21st just hours before the winter solstice. In addition to being the Blue Moon of 2010, the full moon of November is also known as Full Beaver. The frosty nights of late fall were when fur traders began setting their traps for thicker winter pelts.
Either definition for Blue Moon, the third moon of a season with four full moons, or the second full moon in single month, denotes the quality of odd man out. The Moon however, knows no difference since it was shining long before our concept of time began. Look for this month’s full moon just below the star cluster of the Pleiades.
If you like this article and would like to learn more about nature and the turnings of the Earth click the subscribe button above to receive alerts about future articles.