This article defines the Hubble law in terms of Doppler shift, but it properly ought to be redshift or cosmological redshift. While cosmological redshifts and Doppler redshifts are observationally indistinguishable, they have very different causes. Thinking of it in terms of Doppler effect leads to problems. For instance, Doppler shifts greater than the speed of light are not possible, but cosmological redshifts greater than the speed of light are.
22.214.171.124 (talk) 11:47, 5 January 2016 (UTC) Danny Faulkner
- In the "combining redshifts" section, it states that it's not actually a Doppler shift, but I can see how just reading the lead may be confusing. Primefac (talk) 15:31, 5 January 2016 (UTC)
Hubble acceleration scaleEdit
I've seen in various astrophysical papers mention of the "Hubble acceleration scale" a0 = cH0 ≈ ×10−10 m/s26.59. I'm guessing this is the gravitational acceleration requires to bind objects together against Hubble expansion, but all the sources I can find are rather technical and don't have a good WP-level explanation of the significance of the number.
It sould definitely be nice to have a subsection on this value. Has anyone got a simple explanation? 126.96.36.199 (talk) 23:36, 11 November 2016 (UTC)
How did Hubble determine distances?Edit
Correction of Hubble law by German astronom Walter BaadeEdit
The observations of German astronom Walter Baade led him to define distinct "populations" for stars (Population I and Population II). The same observations led him to discover that there are two types of Cepheid variable stars. Using this discovery he recalculated the size of the known universe, doubling the previous calculation made by Hubble in 1929. He announced this finding to considerable astonishment at the 1952 meeting of the International Astronomical Union in Rome.
--AustEngla (talk) 00:25, 11 December 2017 (UTC)