Hennig, R. (1975). Os grandes enigmas do universo. Bertrand.
Lua i Stíl Chicago (17ú heag.)Hennig, Richard. Os Grandes Enigmas Do Universo. Bertrand, 1975.
Lua MLA (8ú heag.)Hennig, Richard. Os Grandes Enigmas Do Universo. Bertrand, 1975.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.