Rare moon a treat for infant 2010

Next New Year 'blue moon' won't occur again until 2028

Posted: Friday, January 01, 2010

Juneau residents may have missed the partial eclipse of the moon Thursday morning due to an untimely sunrise and moonset, but it's unlikely they missed the brilliant fullness that graced clear skies New Year's Eve.

James Poulson / Daily Sitka Sentinel
James Poulson / Daily Sitka Sentinel

But this was no ordinary moon.

It's uniqueness stems from the rare alignment of both the lunar calendar and solar calendar and it's popularity from folklore.

Jason Ginter, a volunteer with the Marie Drake Planetarium, said the "blue moon," as it's called, is when two full moons fall in the same month.

In this case, the first full moon was on Dec. 2.

And Ginter said, it's all about timing.

"The lunar month is a little bit shorter than a calendar month, about 29 days, which is how 'blue moons' are even possible," he said. "It's very rare for the dates to match up like this."

How rare?

"Well, once in a blue moon," Ginter said.

But by the numbers, they occur every 2.5 years. The last time there was a lunar double-take was in May 2007. The next is scheduled for August 31, 2012. But New Year's Eve blue moons are even rarer and occur every 19 years. The last time this combination graced the skies was in 1990; the next one won't come again until 2028.

Despite it's descriptive name, a blue moon doesn't actually turn blue. The name, however, came about after a writer for Sky & Telescope magazine in 1946 misinterpreted the Marine Farmer's Almanac and labeled a blue moon as the second full moon in a month. In fact, the almanac defined a blue moon as the third full moon in a season with four full moons, not the usual three. In folklore, too the name appears. Each moon was named according to its time of year and a moon that came too early had no name, so it was called a "blue moon."

Lunar eclipses, on the other hand, happen somewhat frequently, Ginter said.

"A couple times a year and always when the moon is full," he said. "It's when the earth passes in front of the sun and blocks the light that's going to the moon. Then there's a partial eclipse, which means that it wasn't blocked completely. Usually the moon will go sort of reddish because of light refraction around the earth. And sometimes a partial (eclipse) will make it look like there's a big chunk missing from the moon."

But this particular lunar eclipse was one Juneau residents were not able to see. Nikki Becker, a hydro meteorologicial technician with the National Weather Service, said our moonset this morning was at 8:19 a.m. - about four minutes prior to the sunrise and when the partial eclipse was scheduled to occur.

Anchorage residents, however, were able to see the event. The Associated Press reported that the eclipse was visible between 9:52 a.m. and 10:52 a.m.

Ginter said there are no other notable events scheduled with celestial bodies on the horizon. He did say, however, that the frequency of the aurora borealis, a phenomenon caused by sun spot activity, may be on the rise in coming years.

"We're at the bottom of a 11-year cycle," he said. "It's only just beginning to pick up."

• Contact Outdoors editor Abby Lowell at abby.lowell@juneauempire.com or 523-2271. The Associated Press contributed to this report.

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