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Holiday calendar: Snaky Colorado River tricks the eye

The Colorado River twists through Utah in a picture captured by DigitalGlobe's GeoEye 1 satellite on April 22. DigitalGlobe

Is this a dragon snaking over the slopes of the Lonely Mountain, as in "The Hobbit: The Desolation of Smaug"? Actually, you're looking at the Colorado River snaking through Canyonlands National Park in Utah. It's just the orientation of the picture from DigitalGlobe's GeoEye 1 satellite that makes you think the river's gray surface is rising up from the rock.

Our eyes are good at perceiving patterns of shadow and light as a three-dimensional scene, even if we're starting with two-dimensional information. But turn the perspective around, and our eyes are tricked. Such is the case here. The optical illusion has drawn lots of comments on DigitalGlobe's Facebook album. "Try as I may, I can only see the river above the land," one viewer said. Another remarked: "It's like a dragon's body ... look at the feet!"

Rotating the image 180 degrees can reset your perspective to see the river cutting through the canyon.

This is just one of DigitalGlobe's top 20 satellite images of 2013. Check out the full album to see all 20, and cast votes for your favorites by tapping Facebook's "like" button. The top five as of Tuesday will be put up for a final round of voting to pick the top DigitalGlobe image of the year.

We've been featuring some of the top 20 in our Cosmic Log Space Advent Calendar, which highlights daily views of Earth from space during December. Sample the goodies we've already shared, and for more, take a look at The Atlantic's Hubble Advent CalendarZooniverse's Advent calendar and the Galileo's Pendulum Science Advent Calendar.

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.