It’s getting to be my favorite time of year again: summer means astrophotography and I’m hopeful to get out and get some great shots within the next month or so. And to get myself geared up and excited, I combed back through some of my older shots and found, much to my surprise, that my last shots of the Milky Way from Mt. Rainier were concealing an unexpected gem. Here is the original shot:
Looking a little bit more closely at the upper left corner:
The hazy oval object in the photo is none other than our nearest neighboring galaxy, Andromeda, as confirmed by astrometry.net:
Located 2.5 million light years from our own Milky Way galaxy, Andromeda is an enormous spiral galaxy, and our closest galactic neighbor. This makes it easy fodder for amateur astrophotography. Keep in mind, this photo was taken with a 24mm prime lens; Andromeda is visible to the unaided eye in dark skies. That means even a modestly long focal length can result in some fairly amazing shots.
However, before you grab your 300mm lens and race out in search of dark skies, there are two technical issues that complicate using longer focal lengths for astrophotography: relative motion of the stars and the necessary change in aperture that accompanies longer focal lengths. These concepts are covered in considerable detail in my wide field astrophotography post from a couple of years ago.
In order to overcome these issues, it is generally necessary to have a tracking mount to accommodate longer exposure times. If you happen to have a telescope with a tracking mount, you are in luck, as you can just attach the camera to the mount. If you don’t have the luxury of this though, you are not completely out of luck, although you’re going to need to be creative. I’ve considered the barn door tracking mount as a homemade solution; however, when shooting at longer focal lengths, the tracking is generally not smooth enough to shoot for any real length of exposure. In contrast, for shooting at shorter focal lengths, the barn door is an inexpensive do-it-yourself option that is designed to rotate at very near the rate of the Earth, resulting in fairly accurate tracking over the course of up to several minutes. There are a couple of different variations on this, hand-drive and mechanical-drive, both of which can be done cheaply and easily. But if it’s Andromeda you’re after with minimal equipment, the only really reasonable option is stacking a large number of exposures (e.g. >400) in something like Deep Sky Stacker. You can take a series of short (1-2 second) light frames, then some dark and bias frames (which help the software eliminate the signals due to the electronics within the camera), and stack them to achieve a longer apparent exposure length and a decrease in signal noise (more to come on this in a later tutorial).
In terms of photographing our own galaxy this year, I don’t intend to shoot at Mt. Rainier again, simply because I’ve done so a couple of times already; instead I’ll scope out some new Pacific Northwest locations for galaxy shots to change things up a bit, and be sure to let you guys know what I find; at the present moment, Ruby Beach is high on my list, weather permitting.