The wonder of star trails

Ever since becoming interested in astronomy, I have always enjoyed taking pictures of the night sky. You might think that astrophotography would be an enormously complicated hobby, but actually it is not.

You can obtain beautiful celestial images for yourself using a relatively cheap digital camera fitted with a wide-angle lens and a sturdy tripod. With this kind of equipment, and a little bit of patience, you can take pictures that will really impress your friends and family.

Why not give it a try?

As any seasoned stargazer has observed, over the course of a night, stars appear to change position in the sky. But it is not the stars that are moving, it is the earth.

The apparent motion of the stars is actually caused by the earth's rotation; as the planet beneath our feet rotates on its axis, we see an ever-changing night-sky vista. The aim of star trail photography is to use your camera to capture this apparent motion of the stars.

To take a picture of star trails, attach your camera to a tripod, point it at an interesting part of the sky and make sure it is accurately focused on the stars. For most cameras, an ISO (or speed) setting of between 100 and 800 will get great results.

With camera speed set, and your lens at its widest aperture setting, hold the shutter open for 30 seconds or more. The longer you hold the shutter open, the longer the star trails will be in your final image.

When setting up a star trail image, always try and think about the composition; having a great mountain or harbour in the foreground will make for a much more pleasing picture.

Last week I was lucky to spend six nights at the University of Canterbury's Mount John Observatory. During my time there, when not taking pictures through the telescope, I made sure to set up a couple of cameras looking both north and south to capture some pictures of star trails.

As you can see, the results from long exposures can be extraordinary!

-By Ian Griffin

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