* Fool Me Twice: Fighting the Assault on Science in America. Harmony/Rodale. 11 de octubre de 2011. ISBN 9781609613204
* Fool Me Twice: Fighting the Assault on Science in America. Harmony/Rodale. 11 de octubre de 2011. ISBN 9781609613204
* Hubble, Edwin Powell (1920). Photographic investigations of faint nebulae. Chicago, Ill., The University of Chicago Press
* Hubble, Edwin Powell (1920). Photographic investigations of faint nebulae. Chicago, Ill., The University of Chicago Press
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* Kupperberg, Paul. (2005). Hubble and the Big Bang. The Rosen Publishing Group. pp. 45–6. ISBN 9781404203075. (requiere registro). «World of Physics Hubble»