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 tonight's 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 it does indeed count. 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, back in June, was merely a partial blackout. Total eclipses of the moon are actually less common 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 12 stages of the eclipse 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.
Joe Rao / Space.com
This table indicates which stages of the eclipse will be visible when: 1. Moon enters penumbral shadow; 2. Penumbral shadow begins to appear; 3. Moon enters umbral shadow; 4. 75 percent coverage of moon; 5. Near-totality; 6. Totality begins; 7. Middle of totality; 8. Totality ends; 9. 75 percent coverage of moon; 10. Moon leaves umbra; 11. Penumbral shadow fades away; 12. Moon leaves penumbral shadow. For full details, consult this guide to the 12 stages.
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 us 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 not that great for much of the country tonight, including my neck of the woods in Washington state. (Consult our weather page to check the conditions in your neck of the woods.) Well, there's always the Internet. NASA is planning to stream live Web video of the moon as seen from Marshall Space Flight Center in Alabama. The embedded video coverage will be accompanied by a Web chat with NASA astronomer Mitzi Adams from midnight to 5 a.m. ET Tuesday. Another lunar expert at Marshall, Rob Suggs, will be taking your questions in the same chat forum from 3 to 4 p.m. ET today.
NASA has set up a Flickr group for lunar eclipse photography, and NASA's Jet Propulsion Laboratory will feature one of the Flickr photos as official JPL computer wallpaper. You can bet that SpaceWeather.com will also offer some great eclipse pictures after the event.
Akira Fujii captured this record of the moon's progress dead-center through Earth's shadow in July 2000 by aligning his camera on the same star for successive exposures.
JPL is also offering what it's calling an "I'm There: Lunar Eclipse" social-media campaign for eclipse-watchers. Check out the campaign's Web page 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.
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 total lunar eclipse after that one, 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 Sky & Telescope's Web site for further details.
To learn much, much more about eclipse lore, click on the links below:
- Interactive: What causes a lunar eclipse?
- Nine cool facts about lunar eclipses
- Why an eclipse paints the moon red
- The 12 stages of the total lunar eclipse
- How to watch tonight's lunar eclipse
- It's the best lunar eclipse until 2014
- How a lunar eclipse saved Columbus
- A lunar eclipse ... as seen from space
Update for 3:35 a.m. ET Dec. 21: Sounds like the NASA feed from Alabama is not as satisfying as it could have been, but if you poke around, you'll find other webcasts ... such as this one from Chile.