Irion, R. (2001). Galaxies: Island universes. Reader's Digest.
Lua i Stíl Chicago (17ú heag.)Irion, Robert. Galaxies: Island Universes. Pleasantville: Reader's Digest, 2001.
Lua MLA (9ú heag.)Irion, Robert. Galaxies: Island Universes. Reader's Digest, 2001.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.