A Python 3 script for generating an animation of day length isolines onto an azimuthal map.
Since it's intended as a one-off script, there is no command-line interface and control of the script is via hardcoded constants. Feel free to fork and improve the interface, though.
The script requires the astral module. The base map was generated using this excellent service.
To generate the animation using ffmpeg:
$ mkdir out
$ ./daylen.py
$ cd out
$ ffmpeg -pattern_type glob -i '*.png' -vf scale=-2:720 -c:v libx264 -preset slow -crf 20 out.mp4
Results: