BY NORTH CAIRN

The Portland Press Herald

Additional Photos

A blue moon shines over the Back Bay of the city skyline of Munjoy Hill's Portland Observatory on Sept. 15, 2008 Portland Press Herald photo by Doug Jones

For starters, it won’t be blue.

But it should be easy enough to see the blue moon anyway.

Tonight’s lunar appearance is the second full moon this month. By tradition — some say of several centuries — this second full moon in a single calendar month is dubbed “blue.”

“The blue moon, huh. Very good,” mused Alan Davenport, director of the Maynard F. Jordan Planetarium at the University of Maine in Orono. “I hadn’t even noticed.”

Another definition holds that it is the third of four moons in a single quarter year. Regardless, its allure is that it’s a statistical curiosity, said Davenport. “It’s not an observational event.” Which is to say that this full moon is likely to look pretty much like any other.

It’s not exactly rare, but the blue moon occurs only once every two-and-a-half to three years. One came ’round in 2007, another in 2010.

And now, tonight.

The description blue does not refer to color, Davenport said. The appearance of a hue in the moon is controlled by atmospheric aerosols — particles in the Earth’s atmosphere.

“There’s a long history to the blue moon,” Davenport said. It’s thought that a volcanic eruption or intense, widespread forest fire could blow enough ash into the atmosphere to give the moon a bluish cast. Volcanoes more commonly produce much redder and richer color in the sunsets long after an eruption, he said.

Folklore, Davenport said, for a long time held that the idea of the blue moon came from forest fires in North America that were so vast that they issued enough particles into the atmosphere to make the moon seem blue in Europe.

But no one is expecting that kind of magic here.

“We let them go by,” Davenport said. “We don’t do bonfires or anything.”

Crooners have put their harmonies to the phenomenon. One of the more famous is “Blue Moon,” written by Richard Rodgers and Lorenz Hart in 1935 and recorded by The Marcels in 1961, which attributes a newfound love to the lunar spell.

Contemporary folk singer Nanci Griffith sang a melody tied more to a blue mood than the moon. “Once in a Very Blue Moon,” written by Patrick Alger and Eugene Levine and recorded in 1984 by Griffith, spins the lunar metaphor in a new way, depicting the abandoned lover trying to put a good face on a sad turn of heart:

I found your letter in my mailbox today

You were just checkin’ if I was OK

And if I miss you, well, you know what they say …

Just once … in a very blue moon

And I feel one comin’ on soon

But there are brighter moments planned in Portland for this year’s skylight show. Amateur astronomers, stargazers and geocache adventurers will meet at the city’s Eastern Promenade from 6:30 to 7:30 p.m., to watch the moon rise. Meteorologists predict a hot day, near 90 degrees, will give way to a balmy evening with temperatures in the low 60s.

And then there’s the matter of the lobsters.

The old saw among lobstermen that shedders follow the blue moon is impossible to prove. But, said Ernie Burgess of Chebeague Island, “the moon does affect production, that’s for sure.”

Shedders, he said, are more common in July, unless you’re talking this year, when they turned up in May. But, should greater numbers be hauled after tonight’s blue moon, Burgess said, “the more the better.”

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