Hubble compares distance and recession

Astronomers debated whether spiral nebulae lay inside the Milky Way or farther away. Hubble used variable stars observed at Mount Wilson to support their identification as distant galaxies. Slipher and others had measured spectral shifts, while distances remained limited and uncertain. Hubble assembled these kinds of information and published a comparison in 1929, bringing observations into developing discussion of the large-scale structure of the universe.

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The sample showed a general increase in recession velocity with distance, alongside scatter among individual objects. Spectral shifts and distance indicators each contributed uncertainties to the slope. Hubble and Humason extended observations, and later calibration changed the numerical estimate substantially. The relation could be compared with dynamical cosmological work by Friedmann, Lemaître, and others. Measured positions and spectra became evidence for examining proposed changing cosmic arrangements.

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Expansion models developed through more distant galaxies, background radiation, and additional observations. Measuring the Hubble constant continued as a major task, with differing methods still prompting research. The paper supplied a relationship that theories could address rather than completing all of modern cosmology. Better telescopes, spectra, and distance ladders kept altering estimates of scale and history, making the connection between measurements and an evolving universe a continuing investigative process.

References: [1]