Comet C/2022 E3 (ZTF)

From the last week of January 2023 onwards this comet got high enough in the sky to be imaged in the evening. The weather, however, was not allowing any imaging prior to the 30th. That evening I managed to image the comet using both the SkyWatcher Esprit 80ED and SkyWatcher Esprit 150ED.

Adjacent image was taken with the former between 19:06UTC and 20:01UTC using a ZWO ASI1600MM Pro Cool and ZWO LRGB filters.

Stacked in APP 1.083, post-processing in PSP.

Click here for the full image.

Its distance to Earth this evening was about 0.3AU (44 million kilometres). Further below a second version of this same dataset is shown, now without star-trails.

After the first imaging session it took two hours before the sky cleared enough for a second session, which was done between 21:51UTC and 22:16UTC. The same scope and camera were used, but this time with less and shorter subs were taken to achieve the same goal:

Stacked in APP 1.083, post-processing in PSP.

Click here for the full image.

Then between 22:38UTC and 23:05UTC a third session, now with the Esprit 150ED, was recorded using the same exposures as the second session:

Stacked in APP 1.083, post-processing in PSP.

Click here for the full image.

Above three images all show the comet as it moves relative to the background, causing the stars to trail and showing the order in which the filters were used. Stacking was done each time on the comet in a single pass. Using a threefold processing method it is, however, possible to show the comet as if standing still.

– First stack on the comet, so with Registration Mode on Comet/One Star, and with Integration set to a Median Filter with Kappa High to approximately 1.5. After LRGB-combine this produces a sharp comet with no stars. I will call this [Plate 1].

– [Plate 1] still shows some vague traces, but these can easily be removed with a clone brush. It took me about 5 minutes to clean [Plate 1] a bit further.

– Then stack on the stars with default settings, followed by LRGB-combine, resulting in a starry sky with a smeared comet. This is [Plate 2].

– Pass [Plate 2] through APP's Star Removal Tool, which results in a star-less smeared comet. This is [Plate 3].

– Ran all three plates through Topaz to reduce the noise, but above all to reduce the artefacts left over from the Star Removal Tool, otherwise they will reappear later when combining.

– Load [Plate 3] as a new layer on top of [Plate 2] and set this layer to difference. With this we subtract the smeared comet from [Plate 2], leaving a clean starry sky. This is [Plate 4].

– Load [Plate 1] as a new layer on top of [Plate 4] and set this layer on screen, so that the two layers are combined. This is [Plate 5].

– Then edit [Plate 5] as a normal deep-sky image until it is to your liking.

The end result is what you see here and consists of the same dataset as in figure 1. Due to the long exposure times and tracking on the comet, the stars still are slightly elongated.

Click here for the full image.

On 6 February around 20:24UTC adjacent image of comet C/2022 E3 (ZTF) was taken using the SkyWatcher Esprit 80ED, ZWO EFW mini with ZWO LRGB filters and ZWO ASI1600MM Pro Cool. A total of 196 subs were shot:

In total 44 minutes data.

The comet was at the time of capture in the right-hand part of the constellation Auriga, directly above Saclateni in the direction of the line through Hassaleh and Saclateni. The bright star in the far upper left is HIP23213, the brightest one near the center in the lower part of the image is HIP23799. Its distance to Earth was about 1.2AU (180 million kilometres).

Processing was done as explained above.

The original is here and a trailing-stars version can be found here.

A last attempt to image C/2022 E3 (ZTF) was done on 7 February around 20:05UTC. Again taken with the SkyWatcher Esprit 80ED, ZWO EFW mini with ZWO LRGB filters and ZWO ASI1600MM Pro Cool. A total of 196 subs were shot:

In total 49 minutes data.

The comet was at the time of capture in the right-hand part of the constellation Auriga, about halfway between Hassaleh and Saclateni. The bright star in the tail is Omega Aurigae.

Processing was done as explained above.

The original is here and a trailing-stars version can be found here.