Page "Redshift" Paragraph 10

Beginning with observations in 1912, Vesto Slipher discovered that most spiral nebulae had considerable redshifts.

Slipher first reports on his measurement in the inaugural volume of the Lowell Observatory Bulletin.

Three years later, he wrote a review in the journal Popular Astronomy.

In it he states, "[...] the early discovery that the great Andromeda spiral had the quite exceptional velocity of – 300 km (/ s ) showed the means then available, capable of investigating not only the spectra of the spirals but their velocities as well.

" Slipher reported the velocities for 15 spiral nebulae spread across the entire celestial sphere, all but three having observable " positive " ( that is recessional ) velocities.

Subsequently, Edwin Hubble discovered an approximate relationship between the redshifts of such " nebulae " ( now known to be galaxies in their own right ) and the distances to them with the formulation of his eponymous Hubble's law.

These observations corroborated Alexander Friedman's 1922 work, in which he derived the famous Friedmann equations.

They are today considered strong evidence for an expanding universe and the Big Bang theory.