Edwin Hubble
Henry Norris Russell reads Edwin Hubble's Cepheid paper to astronomers in Washington
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Original prompt & settings (JSON) ↗Hubble was not in the room when astronomy's new scale was unveiled. Henry Norris Russell read the paper for him.
New Year's Day, 1925 — not 30 December
The American Astronomical Society's thirty-third meeting opened in Washington, D.C. on 30 December 1924, the date usually attached to this announcement. Hubble's paper 'Cepheids in Spiral Nebulae' was actually read at the closing session, on 1 January 1925, by Henry Norris Russell — Hubble himself was absent.
Seventy-seven members attended. Nor was the result a secret until then: The New York Times had reported it on 23 November 1924.
Blinking stars as measuring rods
Hubble reported Cepheid variable stars in M31 (Andromeda) and M33, using their period–luminosity relation — discovered by Henrietta Swan Leavitt — to derive distances. By the end of 1924 he had found 36 variables in Andromeda, twelve of them Cepheids, among them the star catalogued V1.
His calculated distance to Andromeda was about 930,000 light-years.
Wrong number, right conclusion
That figure is much too small by modern standards. It was nevertheless large enough, against accepted Milky Way dimensions, to place Andromeda outside our galaxy.
The presentation supplied astronomers with direct distance evidence that at least some spiral nebulae were independent stellar systems rather than objects inside the Milky Way.
Sources
Researched 23 Aug 2026 6 sources 3 audit passes Date corrected
How this was checked
Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →
Date corrected. The research places this at 1925-01-01.
What the sources leave uncertain
- December 30, 1924 was the opening day of the three-day AAS meeting, not the day Hubble’s paper was read. Smithsonian’s National Air and Space Museum dates the formal presentation to January 1, 1925.
- Some retrospective accounts label December 30 the announcement date by conflating the opening of the meeting with the later session.
- Hubble’s inferred distance was much too small by modern standards but was still large enough, relative to accepted Milky Way dimensions, to establish Andromeda’s external location.