How can I get this effect where the stars are seen as lines? Do you need a special camera?
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This technique is called "Startrails" and you don't need to have a special camera.
All you need is:
- time-lapse control to shoot lot's of photos
- fast lens (large aperture)
- startrails software (it's called Startrails.exe and you can find here)
Your camera will shoot for a long time (it depends how is the effect do you wanna get, in your example were about 2 hours). The Compass is necessary to find the earth's axis, it's more beautiful. After you shooting, you have to match them and that's why you need the startrails software. It's very intuitive, drop the pic and click 'start'.
For more information, check this: http://www.lightstalking.com/how-to-photograph-star-trails
There are two ways that you have to do a startrails: a single photo (with a very long exposure) or shorter photos. In my opinion lots of photos are better instead of just one because the a long exposure you can get more errors than the first method. If something goes wrong (unplanned lights) you lose everything, so it's safer to do several photos.
Star trails occur because stars "move" across the sky as the Earth rotates, and so when a camera keeps its shutter open for an extended period of time it will absorb this moving light as light trails. For longer trails, other techniques can be used to combine multiple photos of stars. For example, Adobe Photoshop has an "Apply Image" feature that can be used to combine photos. As edilsonfb points out, however, there are some dedicated software products that focus on combining star images.
The circular pattern occurs due to the fact that the Earth rotates rather than slides across the universe. To get the circular pattern, point directly north if you live in the northern hemisphere or south if you live in the southern hemisphere.