Dec. 9, 2011 at 12:13 AM ET
The calendar may say there's a full moon, but millions of people will be watching for the moon to go dark on Saturday, during the last total lunar eclipse until 2014. And even if you can't see the eclipse in the sky, you can still bring it up on your computer.
The best views will be available in Asia and the Pacific, but the western U.S. and Canada will get in on at least some of the action. In fact, there's a chance that Westerners could see an "impossible" eclipse, with the dark moon and the rising sun in the sky simultaneously.
Lunar eclipses occur when Earth is positioned in its orbit just right to cast a huge shadow on the moon. Unlike a total solar eclipse, which can be seen only along a narrow track of Earth's surface, a lunar eclipse can be seen by half the world. You do have to be in the right half, however.
The show begins with a faint penumbral dimming of the lunar surface at 6:33 a.m. ET Saturday, and reaches its climax at 9:06 a.m. ET with the start of totality. By then, of course, the sun will be up on the East Coast, but folks on the West Coast should be able to see the dark moon over the western horizon. This map from Sky & Telescope can tell you what to expect:
If you're getting up early to see the show, there's no need to get up too early. But you will want to keep an eye on the moon during the 10 or 15 minutes before the onset of totality. That's when you'll see the perceptible darkening of the lunar disk as Earth's shadow creeps across.
The moon doesn't go totally dark during totality. Some sunlight is still refracted by Earth's atmosphere, giving the face of the moon a sunset glow. The precise shade (reddish? brownish? orangish?) depends on the character of the dust and the clouds in the atmosphere. For example, total eclipses tend to be very dark after big volcanic eruptions, as explained in this guide from eclipse expert Fred Espenak.
Over at the NASA Science website, Tony Phillips points out that Saturday's eclipsed moon may look unusually huge to the North Americans who can see it, due to the "moon illusion." It's not that the moon gets bigger when it's near the horizon; it's just that our brain is programmed to perceive sky phenomena differently depending on whether they're overhead or lower down in the sky. This archived article from 2008 explains how it works.
The total phase of Saturday's eclipse is due to last 51 minutes. For North Americans, sunrise and moonset could come before that time, depending on where you live. On the other side of the world, some folks in Europe, Africa and the Middle East will see only part of the show after sunset. In between, most Asia-Pacific observers will be able to watch the whole thing, while South America is out of luck.
But then there's the Internet: Even if you're totally out of the eclipse zone, or facing total cloud cover, you can still experience totality on your computer screen. A remote-astronomy service called Slooh is offering a live eclipse feed from Hawaii, Asia and Australia starting at 8 a.m. ET (5 a.m. PT), with audio narration by astronomer Bob Berman. He'll be joined by several guests and will also take call-in questions. You can use a Slooh app to watch the show on your Android phone, or click on this window:
Here are some other webcast options. If you come across any I've missed, please let me know about them in your comments below; I'll add them to the list if appropriate:
If you snap a picture or capture a video of the eclipse, will you please share it with us? Feel free to use our FirstPerson upload tool, or post it to Facebook, Flickr or YouTube and let me know about it via the Cosmic Log Facebook page. We'll put together a smorgasbord of eclipse pics on Saturday.
It'll be a while before we see such a sight again. Only partial or penumbral lunar eclipses are expected during 2012 and 2013. Our next date with lunar totality comes on April 15, 2014. Don't worry, the world won't end: It'll just seem like it on Tax Day.
More about lunar eclipses:
Don't forget to send along the pictures you want to share by following the instructions above.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.