The first Earth-orbiting solar sail has been caught streaking across the sky. When glints of sunlight reflect off NASA's NanoSail-D satellite, the 10-square-meter sheet of shiny space-age material can briefly outshine the brightest stars.

NanoSail-D unexpectedly unfurled on Jan. 20, after spending a month trapped in its mothership. It is the second solar sail to ever be successfully deployed, and the first to orbit the Earth.

Between now and April or May, the shimmering sheet will skim through the upper atmosphere, slowly descending as it accumulates drag. The idea is to test potential "drag sails" that could help automatically remove future satellites from orbit at the end of their lives, reducing space junk.

Until then, watch the skies. As NanoSail-D sinks closer to Earth, it could flash ten to 100 times brighter than the planet Venus. That's the sort of thing you can see even through city lights.

These flares may be a challenge to spot, though, because of the unpredictable viewing geometry. When viewed edge-on, it's invisible. The sail only glints when the angle with the sun is right. Several websites, including Heavens-Above, Spaceweather.com and Calsky, can tell when NanoSail-D will be overhead, but not when it will flare.

Later in the mission, the best bet for catching a flare is when the sail is near the horizon. Right now the sail is tumbling, so flashes could occur at any time. But as it drags through the atmosphere, it will flatten out, with the flat surface facing forward like an ocean-faring ship. That means it will be edge-on when it's high in the sky, but face-on and likely to flash closer to the horizon.

The beautiful photo above was captured Jan. 30 by Finnish astrophotographer Vesa Vauhkonen. If you can take a better one, submit it to NASA. NASA and Spaceweather.com are sponsoring a contest for the best images of NanoSail-D submitted between now and when the sail disintegrates. You could even win some cash. So look up!

Image: Vesa Vauhkonen/Spaceweather.com

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