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Edwin Hubble Confirms Andromeda as Separate Galaxy

10/6/2025

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Summary

Story summary

On October 5, 1923, Edwin Hubble identified M31-V1 as a cepheid variable, not a nova.
His observations supported Andromeda as a separate galaxy, challenging the Milky Way–only universe view.
The distance estimate placed Andromeda at about 900,000 light-years, later corrected to 2.5 million light-years.
The work drew on Henrietta Leavitt's Cepheid relation and helped establish the expanding-universe view through redshifts.

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Story summary

On October 5, 1923, Edwin Hubble identified M31-V1 as a cepheid variable, not a nova.
His observations supported Andromeda as a separate galaxy, challenging the Milky Way–only universe view.
The distance estimate placed Andromeda at about 900,000 light-years, later corrected to 2.5 million light-years.
The work drew on Henrietta Leavitt's Cepheid relation and helped establish the expanding-universe view through redshifts.