International Space Station enters 2001's star gate

Just because you're sitting in the most expensive bit of kit on the planet (well, orbiting the planet) it doesn't mean you can overcome all the technical glitches of digital photography.

This is what Expedition 31 flight engineer Don Pettit on the International Space Station has found while trying to create star trail photos. Such photos capture the night sky in exposures so long that the imperceptibly slow movements of the stars around the poles become bright streaks. To get this effect using film-based cameras, astrophotographers need to leave their camera's shutter open for 10 to 15 minutes.

However, most digital cameras are unable to have their shutters open for more than about 30 seconds at a time. So instead of one long exposure, amateur star photographers take a series of 30-second shots and later combine them together on a computer. Pettit used this technique to stack 18 photos taken by a stationary camera on the ISS.

Often the appeal of star trail images lies in the sharpness of the foreground - often a remote, still and beautiful landscape - contrasted with the whirling energy of the stars moving above. For Pettit's photo the Earth is spinning past quickly too, and the only still point of reference is part of the space station itself at the top of the photograph.


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