Install wmsun by entering the following commands in the terminal:
sudo apt update sudo apt install wmsun
Description:
Dockable WindowMaker SunRise/SunSet App
wmSun displays the current day's Sun Rise and Set Times. You have to enter your Latitude and Longitude for it to work correctly. wmSun is designed to work with the WindowMaker dock, but will work with other window managers as well.
Homepage: http://windowmaker.org/dockapps/?name=wmsun
Version: 1.05-1build1
Section: universe/x11