Comet 46P / Wirtanen…FINALLY!

At last, after several attempts, a couple of weeks, bad skies, equipment damage (down to my own clumsiness) and malfunctions, I’ve finally managed to capture Comet 46P / Wirtanen on camera.

I’d been sitting down to watch one of the Star Wars movies (Rogue One), and I figured I’d go out and have a smoke first. The weather the past few days has been abysmal with lots of rain and “danger to life” wind speeds, so I wasn’t expecting what I saw when I stepped out of the kids front door – beautiful bright clear skies with Orion shining in front of me, brightly taunting me. Considering that recent weather, it didn’t take much deliberation to decide whether or not to go for it. Winds were still gusting but in between the gusts were reasonable periods of calm. It would’ve been criminal not to try.

Grabbing the ST102 and SW SA rig, I dragged it out front and went through a rapid polar alignment, nailing it first time. Two minutes after switching the mount to “sidereal tracking” the batteries died. I was running on battery power because I’d previously stood on the USB power cable and snapped the port from its position, resulting in it dropping down into the mount body. See what I mean by “clumsiness”?

Very quickly I decided that the 500mm of the ST102 was going to be too long a focal length to try for anything without guiding or tracking capabilities so I swapped the OTA out for the Nikon D5300 with a 300mm lens stopped down to F / 10. Even at that focal length I knew it was going to be a long shot. The 500 Rule only allows for exposures of 1.5 seconds. I was going old school on this, back to basics, before I had the ability to track celestial targets. I dialed down the shutter speed incrementally, determined to push this as far as the equipment would allow. Finally I settled for 3 second exposures. There was still some trailing, but if you didn’t zoom too close into the image then I deemed it acceptable. Now all I had to do was find the damn comet…

One of the biggest benefits of the modern age of astrophotography is the ability to lookup the position of whatever it is you want to capture. I predominantly use an app called “Star Walk 2” for this. Keying in “46P” to the search engine, I was presented with a graphic representation of where it currently is. In this case just below Messier 45, or the Pleiades Cluster. In order to find it though I had to take an exposure and then have a look at the resultant image in the camera LED screen. This is a long winded way of doing it, and I haven’t done it this way in the better part of a year. But within 20 minutes, I’d found that green smudge of the comet.

Honing in and centralising it in the image took another few test shots and making sure I knew which way manually tracking it with small movements to the right ascension and declination of the tripod would move it on the screen. Already I could see cloud rolling in in the distance, but I still managed 105 images of 3 seconds at ISO 10,000. I also took a series of “darks” and “offsets/bias” shots. I didn’t know if I was going to get another chance at this and I wanted to maximise my images.

The image below is the result of this very impromptu session. It’s not the best capture of the comet, but it’s mine, and I’m proud of it.

46P Wirtanen-3

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