Just over a week ago on a Sunday evening (the 29th January) we had some good clear weather but with a (one day past) first quarter moon to contend with. At this time Comet C/2022 E3 was approaching its nearest distance to us and its brightest magnitude (about magnitude 4.5). Since then it has begun to fade and its distance from us is increasing.
I decided to set up my Celestron NexStar 102 SLT on my borrowed HEQ-5 mount to observe it. The setting up all went much better than on previous occasions and I successfully managed to align the polar scope on the pole (it is an equatorial mount). Part of my decision to do this was to see if I could extend exposure times beyond 30s but more of that later. The NexStar has a reasonably wide field of view which makes it ideal to capture the tail of the comet. I began by taking 30s frames of the comet with my D90 camera attached at the prime focus. Here is one such frame:-
I was pleased by how sharp the stars are in this image. The comet at this time was in the constellation of Camelopardalis and just over the border from Draco. It was at a very high declination of nearly +80 degrees and so not far from the pole. This image is about 2.05x1.37 degrees. North is towards the top left-hand corner and East to the top right-hand. It was surprising how fast the comet is moving across the sky during the 13 minutes I was observing it.
The above picture is combination of the first and last frames that I took over this period. The first was taken at 21:28 UT and the last at 21:41. The comet has moved by about 55 pixels during this time and, at approximately 3.44 arc seconds per pixel, this corresponds to 3.2 arc minutes. So it was moving at 0.24 arc minutes per minute or 14.6 arc minutes per hour.
In all I took 19x30s frames (just short of ten minutes, ISO 1600) and combined them in DeepSkyStacker:-
The background stars have disappeared because I have centred the stacking process on the comet and used the median rather than the average. This has helped bring out details in the tail. All the images I have shown are binned x2 and have been modified in Photoshop to bring out the fainter detail. In this image above it is possible to see two tails. The dust tail causes the wedge of brightness that emanates from the comet at the 7 o'clock position. The ion tail can be seen as a thin line that emanates from the comet nucleus at the 3 o'clock position. Closer inspection (click on the image) reveals that this ion tail extends right to the edge of the frame and splits into three parts.
Finally, I did try to get more photographs of the comet a few days later on the 31st January using the same setup. This time I extended the exposure time to a minute with the use of a digital remote control for the camera. This worked well enough but by then the moon was waxing gibbous and the faint detail from the comet was missing. This is a one minute exposure (ISO 800) I took at 20:14 UT:-
The comet was still in the constellation of Camelopardalis at this time having crossed a bit of Draco again.
All text and images © Duncan Hale-Sutton 2023
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