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.
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 8B8B57C1AA716FC2
sudo sh -c "echo deb http://www.ap-i.net/apt stable main > /etc/apt/sources.list.d/skychart.list"
If you want more frequent update with the development version do:
sudo sh -c "echo deb http://www.ap-i.net/apt unstable main > /etc/apt/sources.list.d/skychart.list"
sudo apt-get update
sudo apt-get 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.