Comet C/2021 A1 (Leonard) on New Year's Eve, 31 December 2021.

This is an animated gif/movie of Comet C/2021 A1 (Leonard), stage name Leonardo DiCometrio. The time duration is 16 minutes, 33 frames at 24 fps and each frame advances 30 seconds, meaning time is sped-up by a factor of 720.

You can see how quickly the tail of the comet was moving blown by the solar wind over just 16 minutes. At the same time the comet nucleus is barely but perceptibly moving. Even if you track the comet nucleus and integrate over a time interval as short as a few minutes then you blur the comet tail structure. Therefore, a compelling reason to use a fast optical system (like F/2) for comets.  The movie frame size has been scaled down to 1000 x 1540 pixels (from 2500 x 3850 pixels) to make it a manageable size for Astrobin.

Capture Information

The original data was captured Planet-style as a SER movie sequence using ZWO ASICap. Each exposure was 5 seconds and the average time between frames was 5.23 seconds, so the downloading overhead was 0.23 seconds. The original SER movie went for over one hour but only the first 20 minutes was unaffected by clouds. Flat frames were captured, dark frames were unnecessary and a super bias was used instead.

Comparison with Earlier Processing

Earlier I had published essential the 20 minutes integration version of the data to yield a single image Leonardo DiCometrio (at the full 2500 x 3850 pixel scale — I've copied this to revision C). When integrating for that period there is implicit tail blurring and nucleus trailing, although no-one would have realised. Since I really really like galaxies, then I was happy to see lots of them down to magnitude 19 in the background. This gif doesn't show the same depth and most of these background galaxies are lost in the reduced integration, down-scaling and gif-compression.

Some Technical Information

Each frame is a formed by a sliding untapered (uniform)  window representing an integration time of 300 seconds and the associated frame time (UT) is given by the midpoint of the window.  The sliding window is advanced 30 seconds from frame to frame. The legend shows the actual UT.

Too Much Technical Information

Lots of programming to develop this gif.

A custom PixInsight javascript script written for this image does the processing for each frame: Integration, DBE, HistogramTransformation (EZ Soft Stretch emulation), FastRotation, ABE, PixelMath, HDRMultiscaleTransform, Curves, MorphologicalTransformation, PixelMath to regularised the median background to make it consistent frame to frame.  The script also outputs raw latex/tikz text, which when typeset gives a sequence of legend graphics one for each frame showing the appropriate UT of the frame — using pdflatex and tikzexternalized tikzpictures which are "external/system call" converted to TIFFs (Convert/ImageMagick).  This means latex is run and the folder full of indexed legends is generated.

A second PixInsight script overlays each legend with its associated image frame using a custom adaptation of the standard PixInsight script called ImageInsert.js.

The animated gif is then built using the excellent PIPP, which also does the rescaling and compression to a manageable size. Alas I had to run it on a PC whereas everything else was mac based.