A black and white photo of M31, the Andromeda galaxy. It is characterized by spiral arms and dark lanes of dust and gas, with a bright center.

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1. Robert McNees (mcnees@mastodon.social)'s status on Monday, 01-Jan-2024 15:54:14 UTC Robert McNees

   Edwin Hubble announced #OTD in 1925 that Andromeda and other spiral nebulae were in fact separate galaxies outside the Milky Way, in a paper read to an AAS meeting by H.N. Russell.

   The Universe was far larger than what many astronomers had allowed themselves to imagine. It was more than just our little island of stars.

   Hubble built on observations by Vesto Slipher, collaborated with Milton Humason, and relied on Henrietta Swan Leavitt’s Cepheid variable work to reach this conclusion.