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Holiday calendar: How an eclipse dims Earth

Half of Earth is in position to watch the moon go dark on Saturday during the last total lunar eclipse until 2014 — but what would someone watching Earth see? You can get a good idea from this montage, assembled from images captured by the Defense Meteorogical Satellite Program's F16 satellite.

The picture consists of different slices of our planet's surface, seen at different times before, during and after a total lunar eclipse on Feb. 20, 2008. The rightmost slices show the earliest times, when moonlight was shining down from the full moon and lighting up the clouds in Earth's atmosphere. The middle slice shows the cloud cover growing dimmer as the partial phase of the eclipse progresses. The slice just to the left of that one shows the view during the total phase. Because the moon is in Earth's shadow, no moonlight was being reflected by the clouds. The only illumination you can see is provided by the city lights of North and Central America.

By the time the next slice of image data was recorded, the eclipse had ended, and moonlight was once again lighting up the clouds. To learn more about the temporary blackout, consult this explanation from NASA's Earth Observatory website.

A similar phenomenon will occur again on Saturday. But in my judgment, the view from Earth looking up at the moon is far cooler than the view from space looking down at Earth's darkness. Prime viewing is available from Asia and the Pacific, and the western U.S. and Canada will get in on most of the action. Residents of the eastern U.S. will have to watch over the Internet, however. Totality begins at 9:06 a.m. ET (6:06 a.m. PT, 14:06 GMT) and is due to last 51 minutes. For the full story, check out our viewer's guide.

If you get a picture 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.

This picture serves not only as a warmup for the eclipse, but also as today's offering from the Cosmic Log Space Advent Calendar, which features imagery of Earth as seen from space every day from now until Christmas. Check back on Saturday for another "treat" from the calendar, and feast your eyes on these previous offerings:

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.