Long Exposure Star Trail Photography

I have always enjoyed night photography, and long exposure star trails are up there as one of my favourite types. It takes a bit of dedication and patience to stay up all night, but the results more than justify it.

Where To Shoot

Get away from light pollution if possible. Image by kunel.

Choose a spot as far away from any cities as possible, or at least point the camera away from that area to reduce light pollution.

Avoid shooting star trails during a full moon - the light will overpower the starlight in a matter of minutes.

Long exposure star trails will drain your camera's battery in no time, and the effect is even worse if you are using in-camera noise reduction. If possible, shoot near a power supply so that you can hook up your camera using an extension lead, or alternative take a portable power source (e.g. one that can run off a car battery).

Remember to choose a clear night or you won't actually be able to see any stars!

Setting Up Your Equipment

Use a sturdy tripod and low ISO setting to keep your star trails sharp. Image by dphershman.

You'll need a camera that can take very long exposure photos. An SLR or digital SLR with Bulb Mode is perfect.

Use the lowest ISO setting available (e.g. ISO 100) on your camera to reduce the amount of noise in your final photo.

A tripod is absolutely essential. The sturdier the better, particularly on a windy night.

Use a wide aperture to ensure you capture plenty of light. This will give you brighter trails.

Wrap insulation around your lens to prevent it fogging (particularly bad on very long exposures on cold nights). An ideal, cheap solution is to wrap socks around it and hold them in place with elastic bands.

Optionally, take a star chart or planisphere along to help you identify the North or South star (see below).

Finally, you may want to take a warm coat, a flask of coffee and a good book to while away the time!

Composing your photo

Star trails rotate about the North or South star - position it in your scene to give you the composition you want. Image by dphershman.

The Earth rotates around the north and south poles, so all star trails are centred above them. If you want to position this centre point exactly you'll need to locate the North Star, Polaris (northern hemisphere) or the South Star, Sigma Octantis (southern hemisphere). Your star trails will form a circle around this point, so position it appropriately in your scene.

Long exposure star trails on their own make stunning photos, but you may also want to include some foreground objects. be sure not to place them too close though or they will be out of focus thanks to the wide aperture.

If you do use foreground objects, the ambient light will often illuminate them nicely, but if not consider using them as silhouettes instead.

Exposure Time

A longer exposure time gives longer star trails. Image by Vijnana.

Exposure time is really a matter of trial and error - it can be anything from a few minutes to several hours depending on the conditions.

It is worth bearing in mind that a longer exposure will produce longer star trails, but will also usually dim the brightness of the trails. The stars complete one full rotation in 24 hours, or 15 degrees every hour, but my advice is to concentrate on getting a good exposure, and not worry too much about the length of your star trails.

Start with an exposure time of 5 minutes and keep doubling it until you get a good result. Once you get close to the right exposure time, use your judgement and previous results to decide whether to increase or decrease the exposure time.

That's all there is to it. Long exposure star trail photos are technically quite easy to shoot - the hardest part is staying awake!