Bellow installation procedure uses only command line approach, because this is the simpler way to follow instructions just by copy-pasting the commands in terminal. This instructions are tested with the currently supported versions of Ubuntu.
This use a script with all the required command to setup the repository, If you prefer to do it the manual way please look at the Debian instruction.
bash <(wget -qO- https://raw.githubusercontent.com/pchev/skychart/master/setup_skychart_deb.sh)
At this point you can install the program using the Software Center or continue using the command line with the instruction below.
sudo apt update
sudo apt install --no-install-recommends skychart
sudo apt-get install skychart-data-stars skychart-data-dso skychart-data-pictures
You will also find the Skychart button in the main menu. Please never run skychart as root or with sudo.