Remember when capturing circumpolar star trails was easy?

 

In 1980, when at 19 years of age I first became truly curious about the night sky, I bought a telescope and began to learn the basics of backyard astronomy. Having never looked through a telescope before, it took some time to figure out finder scopes, eyepieces, Barlow lenses, and star charts. Basic nighttime observing skills and tricks were completely foreign to me. For instance, I didn't know that it takes our eyes about 30 to 45 minutes to completely adapt to the darkness. When our eyes are fully adapted, we can see the stars and nebulae much better than we can at first glance as soon as we walked outside. I had no idea that neighborhood night lighting could ruin my night vision, making it difficult to see the stars until I let my eyes become dark adapted again (by avoiding looking at any artificial lights for another 30 to 45 minutes). Nor did I know that moonlight is just as bad! Avoiding the moon and neighbor lights is essential if you wish to catch sight of the Milky Way or see those dim fuzzy nebulae in your telescope eyepiece. Another thing I soon discovered was the effect of a turbulent atmosphere. There are some nights when the sky might be totally clear, but atmospheric turbulence can ruin your view of the moon and planets in the telescope eyepiece. 

The most astonishing thing that I learned immediately about looking at the stars through a telescope was that the earth moves! I aimed my telescope at a planet or star, and in less than a minute, the object drifted out of the eyepiece field of view. Even though I was almost 20 years old, I had never before noticed the speed of the earth's rotation. Just looking up at the sky for a few minutes, it seems as though all the stars are stationary. And I had never before in my life spent more than a few minutes at a time looking up at the starry host. Since I had never bothered to learn the stars and constellations, each night when I looked up at the sky, it was unrecognizable to me. If I looked at the stars for a few minutes one night and then happened to look up at them for a few minutes a month or more later, I didn't realize the stars weren't in their same locations as before.

In fact, the rotating earth became an annoying and unacceptable problem for me in the back yard while using my telescope to study the moon and planets. It was difficult to get a long enough look at anything before I had to unlock the telescope axes and put the object back in the center. And if I wanted to increase the power, the object drifted away before I could switch out the eyepiece or add a Barlow. Then I'd struggle to find the object again with a higher-powered eyepiece that wasn't even focused. I finally replaced my alt-azimuth table-top 60 mm refracting telescope with an equatorially mounted 8-inch reflector that had a clock-drive (or "synchronous") motor. The clock-drive motor on the right ascension axis kept up with the earth's rotation, so my targets stayed centered in the eyepiece for hours rather than seconds. For the first time, my observations could be made without the constant interruptions of having to re-center my targets.

There was a lot for me to learn as a beginning backyard telescope user, but I quickly found out through reading the astronomy magazines that in order to see things better with my telescope, I should replace the eyepiece with a camera. When you look at a nebula in the eyepiece with fully dark-adapted eyes, that first glance is as good as it gets. You may be able to increase your observational skills using averted vision or choosing the correct magnification to see the finest details, but the object itself does not get any brighter, no matter how long you stare at it. That's why using a camera is beneficial. If you expose longer, the photons build up on the film (or electronic sensor) and there are new details to behold! It's like magic! Even the colors that your dark-adapted eyes cannot see will appear, in all their glory, in photographs.

So, in that same summer of 1980 when I got a telescope and began learning about astronomy, I also bought an SLR film camera, and I began to learn about photography. Wow! Trying to learn two complicated hobbies at the same time was not easy! Especially when both of these hobbies are much more difficult to do in total darkness! Not only is it difficult just to see what you're doing with your equipment in the darkness, but low light has significant impacts on both telescope observing and photography. Lens aperture and film ASA (comparable to ISO) settings have their tradeoffs and compromises. And the most problematic targets to photograph in low light are targets that are moving! When shooting celestial targets with telephoto lenses and telescopes, it is essential that you stop that motion with precise tracking and guiding. Otherwise, your images will suffer from motion blur.

The simplest photography setup for shooting the night sky is a camera and lens mounted on a fixed (non-tracking) tripod. Load the camera with a high ASA number film (in the early- to mid-1980s, that would have been Kodak VR 1000 or Fuji 800) for best sensitivity, open up the aperture of the camera lens (f:2.8 or f:1.4, if your lens had those options, the lower the f-number the better), and then use the rule of 500 to determine how long you should expose before stars begin to trail. 

If you're using a wide-angle lens, like, say, a 28 mm focal length, you could expose for about 17 seconds before star trailing becomes noticeable. The rule of 500 (500 divided by the focal length, in this case, 28 mm) is just a ballpark figure. It takes some experimenting. With short exposures like this, you can only expect to record the brightest stars, so a non-tracking tripod is good for taking pictures of the constellations. You'll see fainter stars in your pictures than your eye could see by just looking up at the sky without optical aid. And in some cases, you'll pick up deep-sky objects like star clusters and nebulae. It's fun to "discover" deep-sky objects that way, and then use your photographs like star charts to go out and look at those deep-sky objects with binoculars or a telescope. 

When I made my first attempt to take pictures of the night sky with a 28 mm lens and film camera, I couldn't see the results right away. The film had to be "developed." I didn't have a dark room and didn't want to mess with those chemicals! I needed to send my film to a laboratory that did the developing and would send me back the negatives along with 3 x 5-inch photographic prints. We didn't have Walgreen's in those years. There was no "One-Hour Photo" then. After exposing all 24 frames on my roll of 35 mm film, I sent it off to a laboratory through my local supermarket. The turnaround was about two weeks. Imagine taking pictures with your camera tonight and not being able to see the results for two weeks! During those two weeks, you can't stop thinking about your pictures, wondering how they'll turn out. You have great expectations, but you also have worries. What if my focus wasn't sharp? What if my pictures were under- or over-exposed? What if the laboratory loses my film? All these questions would be answered in about two weeks. In my case, since I was still learning about photography, I had a lot of mistakes to fix while shooting my second roll of film! And many of those fixes were not good enough, requiring further fixes while shooting up my third roll of film. So, I had been shooting pictures for a month and a half and was barely making any progress! No, it wasn't easy to become a photographer in those days! Much less, an astrophotographer!

Star trails, however, became their own genre. When I just accepted the fact that the stars were going to trail and concentrated instead on the landscape below the stars, I began to enjoy taking star-trail photographs. I could get creative with star trails. Star trail pictures were not mistakes or accidents. I made them on purpose. On a moonlit night, I could let the moonlight illuminate foreground objects and landscapes, while letting the stars trail over them.

Pictured here is a small star party of three or four amateur astronomers under the desert skies of Arizona. The camera shutter was left open for an hour or more causing the stars to trail. Anything that didn't move can be seen the clearest. The dome light in the Ford Bronco was not left on the entire time. It came on only briefly and intermittently when something had to be retrieved from inside, during breaks between exposures. Light from our red flashlights (red flashlights preserve night vision) helped to illuminate the telescopes and other things that were part of our regular observing gear. Card tables, coffee thermoses, camera cases, folding chairs, and step ladders. I always used a tarp as a windbreaker, held up with poles that were kept in place with tie-down ropes staked into the ground (seen at right). The sprawling stars of Scorpius trailed over us as they were setting over the southwestern horizon. Antares is the bright trail passing down through the Bronco's windshield. The Stinger stars are above the large Dobsonian telescope. Some Milky Way clouds can be seen in the upper part of the photo.

The most fascinating star trail pictures are, however, like the one at the top of this page. These are the photos that have the camera aimed directly at the North Celestial Pole. Because when your camera is aimed at the North Celestial Pole (or the South Celestial Pole for those living Down Under), the stars don't trail into long straight lines. Stars in this region of the sky are called circumpolar. They spin around the Celestial Pole all night and all day. They never set. What seems like a special trick of photography is actually the simplest feat to pull off! The rotating earth does all the work! 

There is nothing like a circumpolar star-trail picture to illustrate the rotation of the earth. It's a beautiful thing. A picture says a thousand words, as they say. And when all you do is set up a camera on a tripod, aim it at the North Star, and lock the shutter open for a few hours, you get this mesmerizing view of concentric circles, showing you exactly where the earth's tilt axis is pointing. It's art. It's science. It's amazing!

But over the years since I took the pictures on this page, some changes have occurred that make taking star trail pictures much more difficult than it used to be. In fact, the "star trail genre" is now finally making a comeback, through the efforts of people in recent years who have figured out ways to make today's digital-imaging technology produce star trails again. It's a contradiction, of sorts. Not unlike how NASA put men on the moon in the 1960s and 1970s, but now it's taken 50 years to figure out how to do it again!

In the first place, let's talk about the camera technology. In the 1980s, my 35 mm film SLR (single-lens reflex) camera was mostly mechanical. There was a tiny, button-cell battery for the light meter, but everything else about the camera was mechanical. To lock the shutter open for long exposures, I used something called a "cable release." The cable release screwed directly into the shutter button, and when I pressed the button at one end of the cable, it pushed a pin down into the shutter button on the camera that triggered the exposure. If I set the exposure dial to "Bulb," the exposure lasted for as long as I held the button down with the cable release. I could lock the cable release and that would keep the shutter open for as long as I wanted. If I wanted to take star trail pictures, I locked the cable release button down and let the camera expose for a couple of hours. Then I would turn a screw on the cable and release the shutter-button pin, ending the exposure.

With today's Digital SLRs (DSLRs), you can't do that as easily. Their functions are all controlled electronically. Locking the shutter open for hours will drain the camera's battery. Admittedly, I've never locked my DSLR's shutter open for 2 hours, so I can't say whether or not the battery can handle a two- or three-hour circumpolar star-trail photo. But reliance on the battery is just one of the modern hinderances to star-trail photos.

The bigger problem using DSLRs, though, is the sensor noise. The noise in DSLRs is quite low when the exposures are quick and you're shooting in broad daylight. But in low light, images are quite noisy, and the longer the exposure, the worse the noise gets. Astrophotographers use a lot of sophisticated image-processing to remove the noise in their images, but they also get around the long-exposure problem by taking many short exposures and stacking them. This doesn't work well with star trails because during the second or two that it takes the camera to end one exposure and start the next one, a tiny gap will exist in the star trails. Stacking all of your exposures will produce more of a dotted line than a smooth trail of the stars. 

While there exist software fixes to close the gaps, the whole process is still far more complicated than it used to be with film cameras. For one thing, the star trail picture that you used to be able to make on one frame of your roll of film has now become hundreds of separate exposures and that means hundreds of computer files. For example, let's say you use 15-second exposures to record an hour of star trails. That will require 240 images. After shooting the pictures, you're left with hours of computer work to clean and stack your final product.

Another big difference between shooting star trails today versus shooting them in the 1980s is sky brightness. The careless attitude toward using artificial lights in the nighttime hours has caused our cities and towns to have a larger "light dome" at night. LED lights shine brighter and use less electricity, so everybody seems to love adding more and more outdoor lights onto their houses at night. It would be so helpful if all they did was aim their lights downward, to light up only their yards. And if they put cutoff shields on their lights so that the light doesn't go upward or straight out, trespassing into their neighbor's properties like car headlights. 

There are relatively few people who care about keeping the night dark. Why should the others care? They never look up at the stars. After 10 o'clock, they go to bed and don't even need lights shining in their yards. But they leave them on all night anyway. Why not use motion detectors, so that the lights come on when needed, and then go off after a few minutes? Of course, when these light polluters step outside in their yard at night with the dog, they can't see the stars, thanks to their blinding backyard lights. They don't know what they're missing.

Sky glow is a huge problem nowadays for backyard astronomy enthusiasts. Far worse than it used to be. Star trail photos require long exposures, and they turn out a lot better when the sky is dark. City glow washes out long exposures, effectively removing the fainter star trails. To avoid the city glow problem, we have to drive farther away from the city than we used to.

And finally, a problem that I never saw coming is the overwhelming number of satellites that are now in low earth orbit. If people do happen to turn their night lights off, when they look up at the stars, they'll see dozens of satellites crisscrossing the constellations. This creates a mess for long-exposure star trail pictures. Our eyes only pick up the brighter satellites, but photos capture the fainter ones, too. Add to that the number of airplanes flying over, and you've got your work cut out for you to remove those unwanted streaks from your images!

Take a look again at my circumpolar star trails shot at the top of this page. That was a single long exposure on film. In the hours while the camera shutter was held open, no airplanes flew through the camera's field of view, and not a single satellite photobombed it. Our skies were quiet and dark then. We'll never get them back.