If you'd like to try some comet photography, tonight and the next few days are for you. Comet C/2023 A3 (Tsuchinshan-ATLAS) will be in our night skies just after sunset. Happily, you likely have all the gear you need on hand. No fancy tracking mounts, telescopes, or filters are required. A DSLR will do the trick. Yes, stacking and tracking are great, but I'm trying to keep it simple here so you can just go outside and bring back a good photo.
Finding the Comet
It won't be too hard. If you get clear weather, just look to the west, right where the sun just set. When you start to see some stars, you should see the comet just above the horizon. Here in Arizona, where I am, it will be in this position at 6:30 local time tonight.
In, say, Buffalo, New York, its position will be slightly different. As you go north, the comet will get closer to the horizon. As you go south, it gets higher. There are some pretty good charts on the web to help you find your local view.
No one can be sure how bright Comet A3 will be. Some comets start out really bright and then break up. Some start dim and rapidly brighten. Don't expect it to be as obvious as on the star charts.
Last night, I got this image around 30 minutes after sunset. It was hard to see with the naked eye, and as the sky darkened, the comet went lower and finally dipped below the horizon.
As you can see, it was not gigantic, and it was even fainter to the naked eye.
How to Set Up Your Camera
With most cameras, you'll want a longer lens than the wide angle lens I used on my Sony a7 IV. The image above was shot at f/5.6 for 9 seconds at ISO 1,200 with a 20mm lens. One could easily increase ISO, but then noise will start to be a factor.
When considering where to shoot, try to have a pretty clean horizon, but also think about some foreground elements like a lighthouse, a fence, trees, or, in my case, cactus.
I also cropped this image to make up for my wide angle lens, which was a 20mm.
Focus is really important, and while you can shoot wide open, your foreground will be out of focus, lacking depth of field. f/5.6–f/11 works for me, but then you are taking time exposures to get enough light or raising the ISO. It's a festival of trade-offs. With most lenses, you'll get star trails after 15–20 seconds, so try and stay under that. Experiment and take images at different lengths, so when you get back home to edit, you'll have some that work well.
Trying to judge what you've captured in the dark on your camera's small screen is really tough. In the field, I could barely see the comet on my LCD screen, so try a variety of f-stops and exposure times and select the best when you get home.
Tonight (Sunday the 13th) is predicted to be the best night for the comet, as it's the closest approach to Earth. Every night from here, the comet will get higher but dimmer, and the moon will get brighter. It's a lot to juggle to get the best picture.
Predictions are that later this month, the comet won't be in a good place for photography, so if you're interested and the weather cooperates, give it a try ASAP—ideally tonight or tomorrow. Comet C/2023 A3 won't be back for another 80,000 years, so now's the time.
Of course, there will be other comets that swing by every year, but this one is predicted to be brighter than most we see in a decade or so.
Do let us know how you do, and feel free to send us your C/2023 A3 images.
