1. Simon Singh, Big Bang: The Origin of the Universe, (Harper Perennial 2005), pg. 160
2. G. Lemaître, The Beginning of the World from the Point of View of Quantum Theory, (Nature May 1931), Vol. 127, Issue 3210, pg. 706
3. Allan Sandage, Centennial History of the Carnegie Institution of Washington: Volume 1 The Mount Wilson Observatory, (Cambridge University Press 2004), pg. 503
4. Harlow Shapley, Note on the Velocities and Magnitudes of External Galaxies, (PNAS 1929), Vol. 15, pg. 565
5. Walter S. Adams, Contributions to the Mount Wilson Observatory, (CIWY 1928-1929), No. 28, pgs. 101-102