Step-by-step – Stellarium Ubuntu 18.04 Installation

Installing

2. 2. Setting Up Flatpak

   How to Setup Flatpak on Ubuntu 18.04

   Flatpak Ubuntu 18.04 Installation Guide

   Flatpak Ubuntu 18.04 Setup

3. 3. Installing

   Then to Install Stellarium Flatpak App on Ubuntu 18.04

   flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo

   For further Insight see the Flatpak Official Documentation.
   And after:

   flatpak install https://flathub.org/repo/appstream/org.stellarium.Stellarium.flatpakref

   The Flatpak App Setup do Not need the sudo Command because then it Runs confined into a Sandbox.
   However, you’ll be Prompted to Authenticate with your User’s Admin Pass.
   Then Confirm the proposed Setup with ‘Enter’ and Wait patiently until the App is Downloaded and Installed.