How to... use a star tracker

It’s possible to take lovely photographs of the night sky with just a camera on a tripod, but with a motorised mount that tracks the stars as they move across the sky you can do much, much more

Get clearer images of darker or more distant targets

Taking photographs of the night sky and astronomical phenomena has never been easier. Nowadays basic digital SLR cameras take beautiful portraits of the constellations, capture the subtle glow of the Milky Way and catch meteors zipping across the sky. Even the cameras built into our phones can be set to take the time exposures necessary to record conjunctions of the planets, eclipses and even the starry sky itself.

But there is only so much they can do; if you want to capture really faint objects or take very detailed images of the constellations and the Milky Way you need to find a way to take much longer exposures. The problem here is as the Earth turns beneath our feet the stars, planets and other objects in the heavens appear to move across the sky, so unless you can find a way to follow them they will be recorded as trails on longexposure photos…

Astronomers used to get around this by attaching their cameras to their telescopes as they tracked the sky. Today there are now small motorised mounts that can track the sky independently simply from the top of a tripod, and they can give superb results.

There are lots of different tracking mounts available, but they all work along the same principle: they mechanically turn a camera mounted on them at the same rate as the stars revolve around the Pole Star, thus allowing an astrophotographer to take exposures of up to several minutes in length, more than long enough to capture amazing detail along the glittering trail of the Milky Way, faint comets and nebulae.

Whatever its make, the tracker needs to be mounted on a very sturdy tripod because they are usually fairly heavy pieces of kit.

Then a camera needs to be fitted to the tracker via a ball mount, which will allow the camera to be aimed at any point in the sky. The tracker then needs to be manually aligned with the Pole Star, either by sighting on Polaris through a hole in the unit or by lining up on it through the tracker’s own small finder telescope. These usually have illuminated sighting circles inside them to assist with alignment, and it’s worth downloading a ‘Polaris Finder’ phone app that supports your particular unit to ensure extraaccurate polar alignment using those circles.