Star trails are caused by the earth’s movement. As the earth rotates on its axis, it appears that the stars (and the sun and moon) are revolving around us. To illustrate this, if you stood up and turned in a circle, it would appear that the room in which you were standing was circling around you. In reality, however, it is just your movement that caused this.
Another important concept to understand about stars is that if you stood on the North Pole and looked straight up, the area directly overhead in the sky is called the North Celestial Pole (NCP). The star at the NCP is Polaris, also known as the North Star. Because it is almost directly above the North Pole, the North Star’s position barely changes over the year, and the circular motion caused by earth’s rotation is almost imperceptible, which is why Polaris is so useful for navigation. A South Celestial Pole (SCP) also exists, but the brightest star located there is barely visible to the human eye, so it is not useful for navigation.
How is this knowledge useful in star trail photography? For one, if you point your camera at Polaris, you will get arcs around it. Secondly, the arcs will get longer as you move away from the North Star, until you hit the Celestial Equator, the area of the universe directly over the Equator. After that, the star’s trails begin to shorten again. It is quite simple to find Polaris if you live in the Northern Hemisphere. It is as many degrees above the horizon as the latitude at which you live. For example, if you live at 45o North, Polaris will be 45o above the northern horizon. Your fist at arm’s length is approximately 10o.
The equipment needed to photograph star trails is a bulky setup:
1. A sturdy tripod: A tripod is almost as essential to taking star trails as is the camera. Without a tripod, long exposures are impossible.
2. SLR camera with “BULB” mode: BULB is a setting that lets you keep the shutter open for as long as you hold the shutter button down. This is useful because you can start and stop the picture taking process whenever you want. Otherwise, you could only do a maximum exposure of 15 or 30 seconds, which will not capture major star trails. Only SLR cameras offer this setting. No point-and-shoot cameras that I know of offer BULB.
3. Wide Angle Lens: A wide focal length of 35mm or wider is recommended for capturing as much of the sky as possible. Use the widest aperture you can.
4. Lens Hood: This will make the picture more saturated, especially when photographing near major light sources, such as floodlights at night.
5. Remote Control: Although it would be possible to hold down the shutter button for 15+ minutes, the pictures will be sharper, and it will be much easier to use a remote. Remotes vary from simple models that just have a locking button, to complex remotes that not only have the locking shutter button, but also other controls such as a self timer, exposure length (requires camera being set to BULB) and some other features.
6. Fresh Battery: Each night, start with a fresh battery. Using a battery grip is an excellent alternative. This accessory mounts onto the base of the camera and can power the camera using multiple batteries. Also, be aware that the duration of Long Exposure noise reduction’s processing is the same as the length of the actual exposure. If, for example, the actual exposure is 75 minutes, then the Long Exposure NR (noise reduction) will also take 75 minutes on top of the actual exposure. The total duration of the exposure and NR will be 150 minutes in this case. Experiment until you find out how long your battery can hold out. Mine can take about 113 minutes exposure/113 minutes NR. This is important so that I do not set the exposure for too long and the battery dies in the middle of it causing me to lose the picture.
7. Microfiber Cloth: A soft microfiber cloth is necessary for keeping the lens free from condensation, especially if you live in a humid area. Use a cloth meant for wiping glasses’ lenses. The lens is sensitive and may scratch easily.
Star trails may take lots of experimenting.
1.Know how long it takes to create star trails in each area of the sky
2.Know how long the camera battery lasts, both with and without noise reduction “ON”
1. Choose a location far from light pollution.
2. It should be a clear, moonless night.
3. If there are any bright lights in the vicinity, aim away from them, or use a lens hood.
4. Use trees sparingly to compose the scene. Too many trees may detract from the photo.
5. Set up tripod and ensure that it is stable.
6. Mount camera on the tripod.
7. Plug the remote’s cord into the camera.
8. Verify that the battery is fresh and the memory card is empty.
9. Check settings.
10. Begin exposure.
I usually use ISO 100-200. Note that as it gets colder, the camera will not produce as much noise in the photos. If it is -10 or -20 outside, I could maybe use ISO 400 and a 10 minute exposure with no NR at all! Manual focus your lens to infinity (the farthest away it can focus) because AF will not work at night. You may need to periodically check between exposures that the lens is free of moisture. DO NOT use protective filters. They will produce concentric circular patterns near the center of the image. I have used LED headlamps to light foreground elements such as trees. Experiment until you get it right and have fun!
Another method of star trails photography is taking multiple exposures of, say, 5 minutes (don’t use any NR). After you take a bunch of these short photos, download them to the computer and stack them into one photo. The software I use can be downloaded for here. It is very simple to use. It can also be used to create time-lapse videos, which is also lots of fun.
Since I began star trails photography, I have become more and more amazed at how incredible the universe is. The uncountable mass of stars is quadrillions of miles away at the closest, besides the Sun which is 93 million miles away. This shows the incredibility of our Creator, the need for an Intelligent Designer and how it would be impossible for all of it to have come into being by chance, from nothing, by itself.