Blue Moon: Blue, Blue, Blue

When two full moons occur within the same month, the second is called a “blue moon.” The infrequency of the occurrence has made it a subject of folklore as well as scientific investigation. A common expression is “once in a blue moon,” that is, rarely.

Most years twelve full moons occur, approximately once monthly, over the course of the year. But the common calendar (called the Gregorian calendar) is not precisely aligned to the lunar cycle. Thus every two or three years there is an “extra” full moon.

Various explanations are given for this full moon’s designation as “blue.” One is that in Old English belewe can mean either “blue” or “betrayer.” Because early clergy were responsible for calculating the date of Easter based on the full moon, some years they may have needed to explain whether a particular full moon was actually the “Lent moon” or a false one, a “betrayer moon.”

Are blue moons actually blue? Rarely. But certain moons, not necessarily full moons, in past ages did seem to be bluish in color. The perceived color change probably was the result of other substances in the atmosphere, such as dust or ash from volcanic eruptions. One story is that in December 1883 geologist W. Jerome Harrison reported viewing an “electric-blue” crescent moon against a copper-colored sky from his home in Birmingham, England. He attributed it to lingering atmospheric debris from the explosion of Krakatoa, a volcano in Indonesia. Krakatoa’s spectacular eruptions began in May 1883, culminating in the destruction of the volcano island in August that year. In addition to the volcanic explosions, subsequent tsunamis devastated the region.

Blue moons also have been the subject of popular songs, often with blue given the connation of sadness, sometimes mixed with the sense of rarity. The most popular example is Rogers and Hart’s “Blue Moon,” which begins: “Blue Moon, you saw me standing alone, / Without a dream in my heart, / Without a love of my own.” But then a new love comes along, and the song includes the line, “And when I looked the Moon had turned to gold.” When the tune was first composed by Richard Rogers, it was given different lyrics and originally intended to be sung by Jean Harlow in the 1933 MGM film, Hollywood Party, which featured a number of the movie stars of the era. The song went through other versions — for example, repurposed for the film, Manhattan Melodrama in 1934 — until Lorenz Hart finally gave it the familiar lyrics after that film was released. Since 1934 “Blue Moon” has become a standard ballad, recorded by popular singers including Ella Fitzgerald, Frank Sinatra, and Elvis Presley.

There also is the bluegrass song, “Blue Moon of Kentucky,” written by Bill Monroe in 1947, in which the blue moon is told to “Shine on the one that’s gone and left me blue.” Monroe, often called the “Father of Bluegrass,” is credited with popularizing the genre, which takes its name from his band, the Blue Grass Boys. Monroe’s home state of Kentucky has the nickname, the “Bluegrass State,” based on the prevalence of bluegrass, a smooth meadow grass of the Poa genus. Bluegrass seedpods turn from green to a purple-blue hue, which gives this grass its name.

A blue moon rising on New Year’s Eve welcomed in 2010. The next blue moon should occur in 2011 — plenty of time for any aspiring folklorists or songwriters to get a new composition ready.