After weeks of buildup, it's finally time to go outside and see the full moon go dark — or, if it's cloudy, watch the total lunar eclipse over the Internet.
Such eclipses occur when Earth gets precisely between the sun and the moon, casting a shadow that covers every bit of the moon's disk. North Americans should have the best seats in the house for the event, which reaches its climax at 2:41 a.m. ET Tuesday when the total phase begins. For more than an hour, the moon should glow sunset-red, thanks to the light refracted by the edge of Earth's atmosphere.
This eclipse is notable because it takes place just hours before the December solstice, which marks the beginning of northern winter and southern summer. The last Dec. 21 total lunar eclipse occurred in the year 1638. (Number-crunchers quibbled for a while over whether that one counted as a solstice eclipse, due to shifts between the Julian and Gregorian calendar, but the current consensus is that . The next winter solstice eclipse is due in 2094.)
The timing of the solstice is a coincidence, but it does mean the moon will be riding high in the sky — which should enhance the viewing experience.
The last lunar eclipse, , was merely a partial blackout. Total eclipses of the moon are actually than total solar eclipses — that is, if you don't count faint penumbral lunar eclipses. But while the sun's totality is visible only from a narrow track of territory, usually in a remote area, total lunar eclipses are theoretically visible from an entire half of the world at once. Weather permitting, more than a billion people could see tonight's phenomenon.
Now how cool is that?
"Actually it's a little less cool than people are making it out to be," Neil deGrasse Tyson, director of the Hayden Planetarium in New York, told MSNBC. Tyson pointed out that the eclipse proceeds slowly, starting with the first contact of Earth's shadow at 12:29 a.m. ET. From start to finish, the go on for about five and a half hours. "I don't know how many people are going to stay awake in the cold, winter night to watch the thing," Tyson said.
The best strategy is to get a glimpse at the full moon every once in a while, then find a nice dark place to keep watch starting at about 2:35 a.m. ET (which would be a reasonable 11:35 p.m. PT for West Coasters). You can see the moon go dark, catch sight of the smoldering reddish glow, and then go back to bed when you've seen enough. At 3:53 a.m. ET, the moon comes out of Earth's shadow, which is another highlight of the event.
There's no need to drag out a telescope: Lunar eclipses are best appreciated with the naked eye, or a good pair of binoculars.
But what if it's cloudy? The weather outlook is for much of the country tonight. (Consult to check the conditions in your neck of the woods.) Well, there's always the Internet.
NASA is planning to of the moon as seen from Marshall Space Flight Center in Alabama. The embedded video coverage will be accompanied by a Java-enabled with NASA astronomer Mitzi Adams from midnight to 5 a.m. ET Tuesday. Another lunar expert at Marshall, Rob Suggs, is taking your questions in the same chat forum from 3 to 4 p.m. ET today.
NASA has set up a for lunar eclipse photography, and NASA's Jet Propulsion Laboratory will feature one of the Flickr photos as . You can bet that will also offer some great eclipse pictures after the event.
JPL is also offering what it's calling an "I'm There: Lunar Eclipse" social-media campaign for eclipse-watchers. Check out the for details on what to do and what you'll get. If you're sending out updates via Twitter, include #eclipse and @NASAJPL in your tweets and they just might show up in the live comment stream.
In addition to the eclipse, the night sky offers plenty to look at, including the , a in evening skies and a in morning skies.
The moon's next brush with totality comes next June 15, but North Americans will miss out. West Coasters should be able to spot part of the next total lunar eclipse on the schedule, on the morning of Dec. 10, 2011, until it's interrupted by moonset and sunrise. The next good opportunity for North America comes on April 14-15, 2014. Check out for further details.
To learn much, much more about eclipse lore, click on the links below:
This report is an adapted version of a Cosmic Log posting. Connect with the community by hitting the "like" button on the or following msnbc.com's science editor, Alan Boyle, on .