Comet C/2021 A1 (Leonard)

My objective was to image Leonard with the NP101/60Da.

The temperature was about 38 degrees at the start of the session and had dropped to 35 by the end. I was dressed warmly with battery warmers in my boots and chem warmers in my gloves. The air was still save for an occasional very slight breeze. Dew was not present at all. I did note some high clouds to the distant north that I thought were worth keeping an eye on, but they did not become an issue.

This observing session actually started on Friday morning when I returned from Carrs Mill. The last thing that I did before going inside was to see if Arcturus (and Leonard) were visible above the trees. I estimated that the comet had cleared the trees at around 0400.

This morning I woke up shortly before 0300, and I found the sky to be completely clear. I had not set an alarm because the forecast didn’t look so good. 

I got dressed and was at the scope by 0330. In the interest of time, I elected to try to get a good PoleMaster alignment instead of trying to get PHD up and guiding. I think this worked because I was not seeing elongated stars in my 40 second frames.

My slews were maybe 20 degrees off target, and I couldn’t figure out why. I abandoned the troubleshooting effort and then tried manually slewing to Arcturus thinking that if I could star align on it that I could slew to the comet. I have no finder or Telrad on the 4″, so that was causing problems. I never saw Arcturus, but just when I thought that I couldn’t buy a break found the comet in the frame. 

It took me just a few minutes to settle on exposure values. I put the histogram spike at 33 percent with ISO 1600 and 40 seconds. I thought about going ISO 3200 and 20 seconds to reduce elongation, but that would have doubled my number of exposures, and along with that the number of read noise injections would double, and I would have double the number of 8-second unproductive download times. I closely checked a 40 second exposure and couldn’t detect any elongation, so I went with that. I started snapping light frames at 0402.

Wondering how long I would be able to image, I checked the beginning of astronomical and nautical twilight and found that they were 0536 and 0608 respectively. I was pretty sure that I could go for some time longer than 0536, but I wanted to know how much longer. It occurred to me that as long as the histogram spike stayed at 33 percent that I was clear to keep imaging, so I started monitoring the spike at the beginning of astronomical twilight. The spike stayed steady until it started moving to the right at 0600.

I captured 75 frames. I could see the tail extend almost 1/4 the length of the frame in the BYE display. I inspected one in Photoshop and it looked pretty good, so I am looking forward to working with the data.

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