Photo taken on December 31, 2009 at 7:45pm (straight from the camera)

On New Year’s Eve, look up for a rare sight: There will be a full moon, the second in the month — a phenomenon known as a blue moon.

Blue moons come about because the solar and lunar calendars don’t match, said Mark SubbaRao, director of the Space Visualization Laboratory at the Adler Planetarium. A year has about 11 more days than it would if every month were a lunar cycle of 29.5 days.

The blue moon won’t actually be blue. It may have been given that name to denote its rarity — the phrase “once in a blue moon” dates at least back to Shakespearean times. Or it may be a reference to clergy, who used the moon to calculate the dates for Lent and Easter, calling a moon that arrived too early a “betrayer” — in Old English, “belewe” — moon.

But it will be especially beautiful, says backyard astronomer Art Maurer of Crete, because of the confluence of several factors.

First, Earth will be close to its Jan. 2 perihelion, the point during the year when the planet is closest to the sun.

“When we are a little closer to the sun, we (Earth, if not Chicago) get more sunlight and so does the moon,” SubbaRao said. “So the moon will be brighter.”

Second, the moon will almost be at its Jan. 1 perigee, the monthly phase when it is closest to Earth. “When the moon is at perigee … it appears to be seven percent larger than average,” SubbaRao said.

And third, a full moon rises to a point nearly opposite the sun. Because the sun is low this time of year, the full moon will rise particularly high.

It won’t look stunningly different. But it will be unusual. The last New Year’s Eve blue moon was in 1990; the next will be in 2028.

We’ll only see it if we get another rarity: clear skies.

Article Source:
http://www.chicagotribune.com/news/chi-talk-new-years-eve-full-moondec31,0,6194104.column