Star Trail Photography

How to make beautiful time-lapse photographs of the constellations, and what you can learn from them.


Maybe "Articles" wasn't the best name for this section. I always find myself with miscellaneous stuff which I think is interesting, but which doesn't yet add up to a complete story. I think I need a "Blog" section for all of my less complete, less formal stuff.

Anyway, in the meantime, here's a blog post showing some of my recent attempts to make nice photographs of the constellations. I'm especially interested in making a complete set of time-lapse photos of the major constellations — these result in "star trail" images, in which the streaks of motion show the paths the stars take through the sky. These photos would be similar, and a valuable complement to, my solar time-lapse photos.

All of the following photos were taken in the middle of the Iowa corn fields. The glows on the horizon are farm lights, windmills, and the sky-glow of distant towns.

Constellations

How do you get nice photos of the stars? Using an iPhone or the "full auto" settings of a DSLR doesn't usually work, because the stars are too dim. But if you own a DSLR and are comfortable manipulating the exposure settings of your camera manually, taking nice photos of the constellations is not at all difficult. (There are also apps for portable devices, if you don't own a DSLR, but I don't think the image quality from these is as good.) The main trick is simply to make a very long exposure ... but not so long that the stars move too much. I find 30s is about right for starters. It also helps to widen the aperture, and increase the ISO value, although you don't want to increase the sensitivity too much, because then there will be lots of thermal sensor noise, which appears as "graininess" in the background. The following two pictures are 30 second exposures, with the aperature at the widest setting.

Cassiopeia, Andromeda, and the Great Square of Pegasus
Facing Northeast: Cassiopeia, Andromeda, and the Great Square
Saturn, Jupiter, Sagittarius, Scorpius, and the Milky Way
Facing South: Saturn, Jupiter, Sagittarius, Scorpius, and the Milky Way

Star Trail Photography

Now for the real fun. If you make really long exposures, the stars will move enough that you can see their trails. The maximum limit for my camera is 30 seconds, so I made the following by taking multiple exposures and "stacking" them together. I'm no photography expert, but I understand this technique of "stacking" multiple exposures tends to produce better images than single very long exposures anyway.

The Big Dipper, The Guardians, The North Star, and Cassiopeia
Facing North: The Big Dipper, the Guardians, the North Star, and Cassiopeia
A time-lapse, star-trail photo of Cassiopeia and the Great Square
Facing Northeast: Cassiopeia, Andromeda, and the Great Square

While I was making the following time-lapse photo, somebody drove by in a pickup truck, and I thought to myself: "Oh, great! Now I'm going to have a bright smear through my photo! Well...let's see how it turns out." I actually like the final effect. The truck was driving south, away from me, so the white smear from the headlights wasn't too overpowering, and it was paralleled by a red smear from the tail lights, and the whole effect is quite pretty, in my opinion.

A time-lapse, star-trail photo of Scorpius
Facing South: Scorpius

I have a few problems I need to work out. I really like using a wide angle lens with the star-trail photos, because it is much easier to recognize constellations and to know where you are in the celestial sphere, but very wide fields of view present their own problems. For one thing, the horizon becomes concave, although that may not be that big a deal. On the other hand, you may also notice in most of the photos above that the stars in the center are focused, but the stars near the edges are slightly blurry. I believe this is "coma", due to my aperture being so wide open. Maybe as the year goes on and different constellations present themselves, I'll gain more expertise at creating perfect star-trail photos. If I could make a panorama of exactly the same horizon as my sunrise panorama, showing that the stars and the sun follow parallel paths through the sky...but that's going to require lots of work, and a little bit of luck.


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