Astronomer Edwin Hubble was born #OTD in 1889.
Hubble is best known for combining galactic distance measurements with Slipher’s redshift data to obtain a linear relation between distance and recession velocity. This is now understood as evidence for an expanding universe.
Before that, Hubble used Henrietta Swan-Leavitt's period-luminosity relation for Cepheid variable stars to establish spiral nebulae as separate galaxies situated outside the Milky Way.
In 1923, Hubble took a photographic plate of the spiral nebula M31. It showed what he at first thought was a nova. Over subsequent observations he realized it was actually a Cepheid variable star. He crossed out “N” and excitedly wrote “VAR!”
Using Henrietta Swan-Leavitt's relationship between the period and brightness of Cepheids, Hubble established that M31 was situated outside the Milky Way. Spiral nebula were in fact distinct galaxies.
IMAGE: Carnegie Observatories
This momentous result is only 99 years old. There are people alive today who were born before we understood that the Milky Way is just one of many galaxies throughout the Universe.The current oldest living person, Lucille Randon of France, was 19 years old when Hubble announced this discovery.
