May 25, 2018
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‘Maine rule’ defines tonight’s blue moon

By Nok-Noi Ricker, BDN Staff

BANGOR, Maine — Every once in a blue moon, there is a blue moon on New Year’s Eve.

This is the year, and tonight is the night. The next blue moon that falls on New Year’s Eve won’t take place until 2028.

A blue moon occurs about every two to three years, but a complete moon cycle takes 19 years, Alan Davenport, director of the Maynard F. Jordan Planetarium at the University of Maine, said Wednesday

“They’re not all that rare,” he said. “It’s really an anomaly that happens because of the calendar.”

For more than half a century, it has been popular to call the second full moon in one month a blue moon, but that’s actually not accurate.

A true blue moon is the third of four full moons that occur in one season, either spring, summer, fall or winter, according to Maine Farmers’ Almanac articles printed in the 1930s. That publication no longer exists and is not associated with the current Lewiston-based Farmers’ Almanac.

The definition of a true blue moon given in those articles later was misinterpreted to mean two full moons in the same month, the Lewiston publication’s Web site states.

“For the longest time nobody knew exactly why the second full moon of a calendar month was designated as blue moon,” it says. “However, in the March 1999 issue of Sky & Telescope magazine, author Phillip Hiscock revealed one somewhat confusing origin of this term.”

The custom of calling the second full moon in one month a blue moon stems from an incorrect definition printed in a March 1946 Sky & Telescope magazine article, “Once in a Blue Moon,” according to Hiscock’s article.

In the 1946 article, the author “interpreted what he read in a publication known as the Maine Farmers’ Almanac … and declared that a second full Moon in a calendar month is a ‘Blue Moon,’” the Farmers’ Almanac Web site states.

The Sky & Telescope Web site now calls this misidentified blue moon the “Maine rule.”

Even with knowledge of the misinterpretation, the definition caught on and continues, Davenport said.

“There were times in the past century where there were true blue moons [created from] volcanic eruptions or wildfires that filled that atmosphere and colored the moon,” he said. “Those were true blue moons.”

December’s first full moon occurred on Dec. 2, and the second will rise tonight, just in time for New Year’s Eve revelers and the countdown to Jan. 1, 2010.

“Time to say goodbye to 2009 and toast in a new year and a new decade,” the Farmers’ Almanac Web site states. “While you celebrate this special evening, be sure to take a look at the night sky — not for fireworks but for the full blue moon!”

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