Install hdate-applet by entering the following commands in the terminal:
sudo apt update sudo apt install hdate-applet
Description:
Hebrew calendar applet
A GNOME desktop applet providing an Hebrew calendar that gives the user easy access to the Jewish calendar (including Hebrew date, parasha, sunset and sunrise times, holydays and moon phase).
Homepage: http://hdateapplet.sourceforge.net/
Version: 0.15.11-2build1
Section: universe/gnome