When close to both their perhelion and to Earth, comets can have a fast motion relative to the background sky. This is also the time when they are the brightest. If using very fast optics (the C11 + hyperstar, at f/2 for 280mm of aperture is well suited), it is possible make a video of their movement in the background sky. I have played with this a few times, Comet 46P gave me the best results so far.
By the same token, Jupiter rotates in less than 10 hours (that is a Jovian day lasts 10 hours), so it is possible in a (lucky) night to record an entire rotation of the planet (at least when near opposition). Then the images can be put together to make a movie. Below is an example. That night I struggled a bit with mediocre visibility (very faint clouds passing above my observing location) and Jupiter was a tad low on the horizon, but here it is.
Doing those kinds of movies can get a bit involved, so here is a short outline of the workflow, to be adapted to your needs:
- get some high quality frames at a fixed interval. For comets it involves stacking a few 30s frames around each target frame. For planetary imaging, doing some lucky imaging, from video, at fixed interval.
- For the former I used some scripting in Pixinsight, and for the latter the batch functions of Autostakker2.
- Then harmonize the luminosity of all the images.
- Then batch process the images in Pixinsight for enhancement (the same process can be applied to a collection of images).
- Last interpolate between the frames using optical flow, in G’MIC.
The key to keep this fun is to use batch processing and scripting, so you test one process on one image, and when happy batch apply it to the rest of the images forming the movie.
The G’MIC part is a bit hackish, so here are my notes. First, you need to update your command definitions (only once):
$ gmic -update
Then to use optical flow to interpolate frames between your images:
$ gmic -w -fade_files IMG*.jpg,30,0,-1,1,output.png
The parameters of this command are, in this order :
- Filename pattern
- Number of fading intra-frames.
- Indice of the first frame
- Indice of the last frame (-1 means ‘last frame available’)
- Frame step (1 is default)
- Output filename (increasing numbers will be appended, like output_0000.png, etc…).
- If you don’t want to have the visualization window, just drop the -w option when invoking G’MIC.
The commands I used, for optical flow interpolation, then combining in a movie:
$ gmic -w -fade_files source-images-1080/*.jpg,7,0,-1,1,gmic-7/nl1.jpg
$ ffmpeg -r 60 -pattern_type glob -i ‘gmic-7/*.jpg’ -qscale 1 nl1-gmic-7-60fps.mp4
I like doing the final image combination to movie in PIPP.