van den Bergh, Sidney (2011). "Discovery of the Expansion of the Universe". Journal of the Royal Astronomical Society of Canada. 105 (5): 197. arXiv:1108.0709. Bibcode:2011JRASC.105..197V.
van den Bergh, Sidney (2011). "Discovery of the Expansion of the Universe". Journal of the Royal Astronomical Society of Canada. 105 (5): 197. arXiv:1108.0709. Bibcode:2011JRASC.105..197V.