For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:lemmy04/openSUSE_Tumbleweed/home:lemmy04.repo
zypper refresh
zypper install stellarium
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:lemmy04/15.5/home:lemmy04.repo
zypper refresh
zypper install stellarium
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:lemmy04/15.4/home:lemmy04.repo
zypper refresh
zypper install stellarium