For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:belphegor_belbel:KDE3:others/openSUSE_Tumbleweed/home:belphegor_belbel:KDE3:others.repo
zypper refresh
zypper install cfitsio
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:belphegor_belbel:KDE3:others/15.6/home:belphegor_belbel:KDE3:others.repo
zypper refresh
zypper install cfitsio
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:belphegor_belbel:KDE3:others/15.5/home:belphegor_belbel:KDE3:others.repo
zypper refresh
zypper install cfitsio