The cosmic redshift we measure using light from distant galaxies is not a Doppler effect but instead is a gravitational redshift. That is the galaxies are not receding from each other but instead they are rotating around a common centre of a geocentric universe. The Doppler and the gravitational redshift equations are very similar to each other but they differ in the coeffient of redshift which is equal to (delta lambda) / lambda in the former case and to (delta lambda/ lambda)^(1/2) in the last case. The Hubble velocity is the radial or the orbital velocity that is the Hubble law describes the rotation curve of the universe.
For the light leaving the surrounding galaxies, the gravitational redshift is very small compared to the redshift caused by their receding radial velocities. The Hubble constant is a result of their receding radial velocities.
@@MichelvanBiezen the velocity we derive from the cosmic redshift is the relative velocity between the source of light and the observer based on the earth including the solar system rotation around the centre of Milky-Way and the rotation of the galaxies around a common centre of a geocentric universe or the so-called expanding universe effect.
Let me first say that your lectures are truly excellent and they are much appreciated for their accuracy. But in this particular lecture, why do you not give any attribute to the earlier work of Lemaître on the expansion of the universe? Some may say that he did much of the work that Hubble later gleaned and profited by. Wikipedia reference below, well worth a read for some perspective on this: en.wikipedia.org/wiki/Georges_Lema%C3%AEtre