Blue Moon of Kentucky, keep on shining

Estimated reading time: 4 minutes

Well, it’s almost a new year, and depending on your definition, there will either be two blue moons in it, or none. Using the Farmers’ Almanac definition of blue moon (meaning the third full moon in a season of four full moons), the next blue moon won’t occur till May 18, 2019. But if you consider a blue moon to be the 2nd full moon in the same month, then we’ve got two of those coming up this year: January 31, 2018, and March 31, 2018. The last blue moon was of the second sort was July 31, 2015. You can’t take the occurrence too much for granted: just under 3% of all full moons are blue moons. Nineteen years from now, in 2037, we’ll again have another Blue Moon in January. And the next time New Year’s Eve falls on a blue moon is 2028!

Blue moon of Kentucky, keep on shining,
Shine on the one that’s gone and proved untrue;
Blue moon of Kentucky, keep on shining,
Shine on the one that’s gone and left me blue.

It was on a moonlight night, the stars were shining bright;
And they whispered from on high, your love had said goodbye.
Blue moon of Kentucky, keep on shining,
Shine on the one that’s gone and said goodbye.
—Bill Monroe, Blue moon of Kentucky (1947)

Monroe wrote the song he’s most known for right on the cusp of an expansion in public understanding of just what a blue moon is. In the 1940’s, astrologists and meteorologists started using the term to describe when the moon takes on a blue coloration. This happens when small atmospheric particles interfere with light, causing a bluish tint to the moon’s appearance from earth. The particles can come from things such as forest fires and volcanic eruptions. However, this only occurs “once in a blue moon.”

More traditionally, a blue moon was referred to as the 4th full moon in a season. Each of the 4 seasons of the year has 3 months, and will usually have 3 full moons. Each of these 12 moons has a name like “Harvest Moon,” “Hunter’s Moon” and so on. When a season occurs that contains 4 full moons, the 4th becomes the blue moon.

Blue moon is different from the monthly or seasonal moon names as it isn’t restricted to a time of year. It is a movable feast that occurs because the moon and our calendar are not in sync and all the months but February are longer than the moon’s cycle.

So just how often is “once in a blue moon?” There are 1,200 calendar months in a century. In the same century, there are, on the average, 1,236.83 full moons. The difference is the average number of blue moons in a century: 36.83, or an average of one per 2.72 years.

Actually, about one year each 19 has two blue moons, because its shortest month, February, has no full moon at all; for the Eastern Time Zone, the complete list of such years from 1951 through 2050 is 1961, 1980, 1999, 2018, and 2037. Between these years, blue moons happen at intervals such as 2 years and 7, 8, 9, or 10 months.

There’s a pretty fair chance that the jilted lover of Monroe’s blue moon song was singing in October, August or July, historically the months with the most blue moons.

So was it the coloration of the moon that reminded the singer of how sad and blue they felt, was the singer comparing the inconstancy of a blue moon to the lover’s inconstancy, or both? Kentucky’s General Assembly offered no answer to this question when, in 1989, it passed KRS 2.100, designating the song “Blue moon of Kentucky” as the official state bluegrass song.

sources:

www.kdla.ky.gov/resources/kybgsong.htm#BlueMoon
www.ips-planetarium.org/planetarian/articles/folkloreBlueMoon.html
www.farmersalmanac.com/full-moon-names
www.skyandtelescope.com/observing/objects/moon/3304131.html?page=1&c=y

More articles on New Year traditions:

New Year countdown(Opens in a new browser tab)

Breakin’ up Christmas(Opens in a new browser tab)

Ringing in the new(Opens in a new browser tab)