Copyright © Michael Hofferber
Some natural events are truly rare, like a total solar eclipse or St. Elmo's Fire.
Seeing Halley's Comet or Hale-Bopp in the night sky was probably a once-in-a-lifetime event, as was the 1980 eruption of Mount St. Helens or movement along the New Madrid fault in Missouri.
These events occur a lot less frequently than "once in a blue moon," as the saying goes, and for this we should be thankful.
A Blue Moon, by definition, is the second full moon in the same month. Because there are 29.53 days between each full moon, a Blue Moon doesn't rise very often. But neither are Blue Moons all that rare. Some years we have two of them.
Blue Moons are a lot like every-other-Friday paydays. Workers paid biweekly know that every once in a while, but certainly not often enough, they get three paychecks in a month instead of the normal two.
Once in a Blue Moon, technically speaking, is a little less than once every three years -- about as frequently as folks buy a new car or consider changing jobs. Two Blue Moons in the same year is unusual, occurring just once in every 19 years or so, but two Blue Moons in three months is truly portentous. Surely its a sign of some significance.
Folklorists can only guess at the origins of the Blue Moon or how it got its name. The Harvest Moon of autumn is often tinged with the colors of its season. The full moon of June is generally goes by the pet name Rose Moon or the Flower Moon, while other folks prefer to call it the Strawberry Moon.
There's also a Green Corn Moon, a Thunder Moon, the Sturgeon Moon and the Moon of Pairing Reindeer. Whatever its origin, the Blue Moon does not necessarily look blue at all. It may be making its appearance in winter one year, but next time around it could as easily rise over ripening wheat fields or preside over spring. It can and does appear any time of year.
Blue-colored moons appeared at sunset for months after the Indonesian volcano Krakatoa exploded in 1883, and the moon in Newfoundland was turned blue in 1951 when huge forest fires in Alberta threw smoke particles up into the sky. These are rare events, and unpredictable, having nothing to do with the lunar cycle or our calendars.
Four hundred years ago, if someone said, "He would argue the moon was blue" it was the same as saying, "He'd argue that black is white." To say that something would happen when the moon turned blue was like saying that it would happen on the Twelfth of Never. And until 1582, when the Gregorian calendar was introduced, that's just how often there were two full moons in the same month.
The Hebrew and Islamic calendars, which define their months by the full progression of lunar phases running 29 or 30 days, have no Blue Moons. Only the modern calendar, whose months vacillate between 28 to 31 days in length, allows room for Blue Moons.