Mount Wilson Observatory in History

Hubble identifies Cepheid variables in Andromeda and shows it lies beyond the Milky Way

Photographs M31 with the 100-inch Hooker telescope and records the star later recognized as Cepheid variable V1 on the famous VAR photographic plate.

Identifies multiple Cepheid variables in M31 and uses their periods to demonstrate that Andromeda is far outside the Milky Way.

Hubble announces evidence that spiral nebulae are external galaxies, expanding the scale of cosmology

Humason begins measuring faint galaxy spectra that later strengthen Hubbles velocity distance relation

Hubble publishes the velocity distance relation that makes expanding relativistic cosmology observationally compelling

Hubble publishes the velocity distance relation showing that galaxies recede faster at greater distances

Humason provides redshift measurements used by Hubble to support the velocity distance relation

Sandage begins revising extragalactic distances and expansion measurements after Hubbles work

Baade distinguishes stellar populations and revises Cepheid distances used in estimates of cosmic expansion

Baades corrections help make the cosmic expansion rate more realistic for Big Bang timescales

Sandage continues refining the expansion rate, an essential parameter for Big Bang age estimates