science · 30 December 1924 · 100 years ago
In 1924, a meeting of scientists began in Washington, D.C. On its last day, 1 Jan 1925, its main event was a paper read by H. N. Russell on behalf of the absent author, Edwin Hubble. Although titled about Cepheid Variables, Hubble's paper gave the first proof that Andromeda was a separate galactic system—an “island universe,” far beyond our own Milky Way, and equally large. Previously, scientists couldn't tell if nebulae (fuzzy clouds of light) were within the Milky Way or not. Hubble measured the distances to Cepheid stars in the Andromeda nebula and showed it was a hundred thousand times as far away as the nearest stars—proof it was a separate galaxy. He wrote a letter to Harlow Shapley on 19 Feb 1923 about his first measurement. New York Times (22 Nov 1924) told the public, before the meeting.
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