Quote:
Originally Posted by wasyoungonce
And I though it was Vesto Slipher working as Hubble's assistant who actually made the discovery of these "currently unknown nebula"...later determined to be external galaxies.  |
Vesto Slipher is definitely very underrated. He discovered that M31 is
approaching our own Galaxy (its light is blueshifted), and he did discover that many galaxies (which would probably have been called spiral nebulae, at that time, as their true nature was in dispute!) are receding from our own Galaxy at high velocities.
However, I was under the impression that, while Slipher had considerable evidence for the general recession of the 'spiral nebulae', he did not discover what is generally known as the Hubble Law or Hubble's Law, which is the proportionality between galaxy distance and galaxy velocity. Hubble had more recession velocities to hand, and he had to make a lot of assumptions about the distances of the galaxies, in order to figure out that the more distant is the galaxy, the higher is its recession velocity. (if we graph the galaxy velocity vs galaxy distance for a sufficiently large number of galaxies, the graph is a straight line, as long as we take into account the individual velocities of the various galaxies)
I don't think Slipher interpreted his ground-breaking data as being due to the expansion of the universe.
A summary of Slipher's work, plus some of his papers, can be found here:
http://www.roe.ac.uk/~jap/slipher/
The early discoveries of Slipher, Lemaitre, Lundmark, Hubble, etc., regarding the expansion of the universe are of the highest importance, and it is obvious that too much of the credit has gone to Hubble. However, Hubble did have enough galaxy redshifts and galaxy distances to conclusively prove that galaxy velocity is proportional to galaxy distance.