Rare, super-large total lunar eclipse on Dec. 10, 2011

On this Saturday, Dec. 10, early risers in Seattle, Portland and other Pacific Northwest outposts may do elongated spit-takes over their small-batch coffees as the moon shifts from its normal ivory hue into an angry orangish-red color more often seen with rotting pumpkins or baboon butts.

Yes, it's time for another lunar eclipse, and this one is bound to be spectacular. The moon will achieve full immersion in the earth's shadow at 6:05 a.m. PST, right at the moment it sets* into the horizon. This celestial timing guarantees that the moon will appear super-large in accordance with the not-quite-understood principle of "moon illusion." So get ready to be wowed... unless you live in Washington, D.C., or anywhere on the East Coast, where the total eclipse will go unnoticed. Here's a visibility map showing loads of :( :( :( for residents of the eastern U.S. on Saturday:

Courtesy of NASA (more technical details here)

This is the last total eclipse until 2014, so D.C.ers are doubly screwed. (It's always helpful to know the dates of upcoming eclipses, as they can be used to score food and favors from begrudging natives, a la Christopher Columbus.) However, there are a few sites that plan to stream the momentous event; here is one broadcasting from the Himalayan foothills. It might be worth watching, because the strange, syrah color of the occulted moon – an effect caused by sunlight filtering through dust in the atmosphere – could be extra eerie this year. According to NASA:

The exact hue (anything from bright orange to blood red is possible) depends on the unpredictable state of the atmosphere at the time of the eclipse. As Jack Horkheimer (1938-2010) of the Miami Space Transit Planetarium loved to say, "Only the shadow knows."

Atmospheric scientist Richard Keen of the University of Colorado might know, too. For years he has studied lunar eclipses as a means of monitoring conditions in Earth's upper atmosphere, and he has become skilled at forecasting these events.

"I expect this eclipse to be bright orange, or even copper-colored, with a possible hint of turquoise at the edge," he predicts.

Keen's forecast is based on the amount of microscopic crud floating around the atmosphere at any given minute. Sometimes there's a lot of crud because of volcanoes pumping out tons of smoke and ash. Eclipses during these times tend to be dark and murky, like old blood. However, the earth is in a downtime at the moment for crud, and the clear skies will likely produce a brighter lunar eclipse.

Now, if you want to know more about that slice of turquoise likely to gild the lunar pie, scroll down to an informative video from the nation's eggiest-headed space nerds. (In a good way.) For an idea of what the western U.S. will see this weekend, there are always photos and a time-lapse video from Dec. 2010's lunar eclipse over the District.

* Not rises! Stupid!