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Holiday calendar: Red and green lights glow in space

NASA via Fragile Oasis

A Dec. 6 image from the International Space Station shows auroral lights below, with a reddish glow on top of the brighter greenish glow.

Red and green are traditional Christmas colors, and they're also the colors of the aurora — as seen in this top-down view from the International Space Station.

"What you can't see in this image is the astonishment on the face of the astronaut who took it [on Dec. 6] as the crew zipped east with northern Europe in view," the folks at Fragile Oasis report in a Facebook posting.

Northern lights take on a reddish or greenish glow, depending on the altitude of the aurora and the composition of the atmosphere. This FAQ file from the University of Alaska explains the physics behind the different colors.

For more astonishing pictures of Earth from space, you can browse through Fragile Oasis' website as well as its galleries on Facebook, Twitter, Google+ and Flickr. You can also catch up on these daily entries from the Cosmic Log Space Advent Calendar, which will continue through Christmas.

Previously on the Space Advent Calendar:

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science 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.