When I was a child, I dreamed of having my own spaceship. I wanted to visit the Moon and the planets, sail among the stars and galaxies. The Apollo space program and a bevy of cheesy sci-fi TV shows fed my childhood daydreams. I never got that spaceship, but I do have a telescope. For the earthbound observer or imager, a telescope can make a pretty effective spaceship — and truth be told, a time machine as well.
If you could travel back and forth to the Andromeda Galaxy at the speed of light, the trip would seem instantaneous to you (thank you, special relativity). Maybe snap a few photos and come right back for dinner. But when you’ve returned, you’d find over 5 million years have elapsed here on Earth, and your dinner is more than just cold. If you still want your dinner to be hot when you get back, you’re going to need to travel in both time and space. No, you don’t need a TARDIS for this, you just need a telescope (not that I’d turn down a TARDIS if you offered me one). Then you can visit all the galaxies your heart desires, before or after dinner.
Astrophotographers often refer to springtime as “Galaxy Season,” but you can get a jump on it now if you’re willing to shoot between midnight and dawn. As the band of the Milky Way sinks further into the west after sunset, we can peer out of our galactic home to look at a sky richly populated with other galaxies many millions of light-years away.
Select the Right Target(s)
Even if you don’t have a largish, long-focal-length instrument or very dark or steady skies, there are still many interesting galaxy clusters that make for great compositions. A handful of large, nearby galaxies are perfectly suitable for small scopes with short focal lengths, even under light-polluted skies. Many more distant galaxies with a moderately high surface brightness can shine through some light pollution.
When imaging from your backyard, you typically need longer total integration times to reduce shot noise from the sky background, but good galaxy images can be had with sufficient patience.
I’ve found — to the surprise of many — that I can photograph galaxies even from the brightly lit parking lot of my neighborhood coffee shop. My secret? I shoot with a monochrome camera in its native black-and-white palette.
Why? Because it takes a lot of work to make colorful galaxies imaged from light-polluted locations to appear natural. Besides the long total integration time, there’s also lots of corrective work due to the complex color gradients introduced by light pollution.
Black-and-white imaging has several powerful advantages when it comes to galaxies. For one, each pixel of your monochrome camera is receiving a little more than three times more signal than a color camera does. That makes for a significant reduction in shot noise (nearly by half, depending on your camera and other factors). And although you are improving the response to the sky glow as well as the galaxy, keep in mind that have to pull these two signals apart anyway — why not improve the galaxy data as much as you can?
Second, it is far easier to manage a light pollution-induced gradient in your image in a monochrome image than it is when you are dealing with red, green, and blue all at the same time. Calibration, noise reduction, and sharpening techniques in post processing are all easier to do in grayscale, plus you eliminate the need for color balancing.
Not only do I recommend monochrome imaging as the best way to learn the ropes, but I often resort to it myself when time is short, or conditions are such that I know a monochrome image is going to be a better final product than if I tried to do a color shot.
If you just have to have color, you can always combine an image taken through a luminance filter, a clear filter that lets in visible light but blocks near-infrared light, with RGB data collected from a dark-sky location at some later point.
Don’t Skip the Flat Fields
Still, no matter what you are imaging under light-polluted skies, you shouldn’t skip the application of flat fields in your image-calibration routine. This calibration step is especially important with galaxies because a strong vignette from a light-polluted sky will throw off the automatic screen stretch of most imaging software. Without a proper flat field applied, it’s difficult to know for sure if you are getting good data or not.
When I was just getting started in astrophotography, I’m pretty sure that I threw out a lot of good data that I had misjudged at first glance. This is all the more true when you are doing live stacking or EAA (Electronically Assisted Astronomy), in which the software applies an automatic screen stretch on the fly while the camera is accumulating images. If you can apply flats on the fly as well, you’ll immediately see a remarkable improvement to your individual exposures.
So, what are you waiting for? The galaxies are calling and, with these techniques in hand, your spaceship awaits.