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Star trails

One subject that definitely needs a tripod.


Still pictures resulting from time exposure photography that show the trails of stars are always fascinating to people. The stars themselves are not responsible for the motion that results in the streaks of light that are recorded on film. The light paths show the movement of Earth in relation to the stars. Think of it as the camera aimed upwards from a large revolving platter, like a merry-go-round, turning beneath a ceiling of unmoving pin-point lights.

This super-long time exposure over several hours shows not only the soft effect of moonlight on the bridge and trees, but also captures star trails in the sky.
This super-long time exposure over several hours shows not only the soft effect of moonlight on the bridge and trees, but also captures star trails in the sky.

Stars are not the only celestial objects that may be recorded on the film, however. Streaks traveling in unexpected directions can be caused by an orbiting satellite, an aircraft’s lights, shooting stars and even fireflies.

Photographing star trails requires:

  • a clear, cloudless night,
  • preferably no moon visible in the sky, and certainly not in the viewframe,
  • a shooting location in absolute darkness, far from the ambient light of a city or traffic,
  • a completely motionless camera while the exposure is being made (requiring the use of a solid tripod), and
  • a fast film, in the ISO 400 to 800 range, or a similar high ISO sensitivity setting in your digital camera.

Photography can done in black and white or color.

Time exposures for star trail images are very long, anywhere from 15 minutes to many hours. The longer the exposure, the longer the star trails. There are no hard and fast rules for exposure settings, since haze and atmospheric moisture can affect the amount of light reaching your film and their amounts can vary so much. But, you might try an aperture setting of ƒ/8 to begin with - see Optimum aperture to learn why. (Some photographers recommend shooting with the aperture wide open.) For the first frame, use a shutter speed of 15 minutes, then make a second exposure of 30 minutes, and a third exposure of one hour.

Although the open night sky can be all that you frame in the viewfinder, pictures of star trails generally have more interest when there is an Earth-based object in the foreground. It can be a landscape, a tree or a structure like a bridge or a building. It may appear only as a silhouette unless there is sufficient ambient light to record its features.

If you aim your lens at the North Star, the star trails will show up as bulls-eye type circular arcs, all revolving around the North Star.

For an unusual look, you can experiment with hand-held artificial light to illuminate the earth-bound object. If you use flash, make sure your flash to subject distance is appropriate for the aperture being used to avoid overexposure. If you use a less-powerful light source, such as a flashlight, be sure you don’t shine it on yourself. Use it to “paint” the tree or building as you move around in the viewframe. As long as you don’t remain in one spot for long, your own image will not be recorded on the film during such long exposures.

If you detect a vehicle approaching and are concerned that its lights could ruin your image, simply cover the front of the lens (without moving it) until the vehicle is out of range. A hat, a large lens case or even a lightproof bag can be used to encircle the lens and place it in darkness. You can use the same technique if you notice that an airplane’s path will bring its lights into the frame. Just block the lens opening until the aircraft has flown past. Be sure to leave your lens open longer - by the same amount of time that you had it covered - to complete the exposure.

The moon's brightness exceeds that of the stars. When photographed using an exposure that would normally reveal star trails, it would be overexposed and blurred due to its motion, causing a
The moon's brightness exceeds that of the stars. When photographed using an exposure that would normally reveal star trails, it would be overexposed and blurred due to its motion, causing a "moon trail"..

You may wonder why we do not recommend including the moon in any image that is meant to show star trails. First, its relative brightness will overpower the scene and make it look almost like daylight when using very long exposures. Second, the moon itself is in motion, and if captured in the viewframe, will show up as a long streak in the sky.