Comets are objects that, when getting close to the Sun warm up and release gas. This gas can be seen as a coma and sometimes also as a tail or even double tail.

A very bright and recent comet was C/2020 F3 NEOWISE, which was visible to the unaided eye and showed a very nice double tail.

The comets shown in this section are all imaged by tracking on the comet. This is done unguided by programming the ephemeris into the 10Micron GM3000HPS and then let the mount do the tracking.

Some of the comet images shown here do not show star trails, but most of them do. The reason for this is that comets move relative to the background. So if multiple images are used to produce one image, we can either stack them by aligning the comet in them (which causes the stars to trail) or by aligning the stars (but that causes the comet to trail). The star trails show the order in which the filters were used. Stacking is normally done on the comet in a single pass, but by using a threefold processing method it is 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.