Sunrise and sunset for Raspberry Pi

I now have two time-lapse "shootings" running at the same time. One is pointing at west and the other at north. After months, i added another Raspberry Pi Zero W to my arsenal, since i developed a reliable setup for this kind of long-term operation. I also got it to work as wireless access point, to make it independent from a router, but still have the option to connect to it. And i made further improvements. For example, i let them automatically adjust the settings according to sunrise and sunset. This way the slow shutter speed is only active if needed, depending on the Earth's position to the Sun, which changes during the year.
The city lights dominate, but compared to earlier, i have with a dynamic timeframe a better chance to catch more stars at night. I let my shell script call engine "rhino" to execute a JavaScript file and do some calculations for when sunrise and sunset take place. Thank you to Matt Kane for his interpretation of Kevin Boone's SunTimes Java implementation of the US Naval Observatory's algorithm. I also got another version to work based on Perl, but installing the module "DateTime::Event::Sunrise" via cpanm takes too long on the Zero W. It only needs to be done once for each Raspberry Pi, but that's not worth it, since there is no gain in speed.
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