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Note that these images are made from many exposures that are then processed and combined, and the total exposure time is given. The individual exposure times were probably long, but I'm guessing on the order of minutes, not hours. (Actually, if you photograph stars with an exposure time that is too long, then you get star trails in the image.)

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Trails appear very quickly, at focal lengths of around 20mm (typical dslr kit lens) they are obvious in 20-30 seconds, with a 100mm lens (start of telephoto range) they are obvious in 3-5 seconds. This of course depends on the res of your camera (I shoot with an 8MP and a 24MP).

To get rid of the trails you need a tracking mount. The better the mount the smoother and longer it tracks. Astrophotography is expensive...

> if you photograph stars with an exposure time that is too long, then you get star trails in the image

He was using a tracking mount. At 200mm you can't image for more than a few seconds without trailing.

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