On Saturday, December 9, 2017 at 2:38:49 PM UTC-6, Brent wrote: > > > > On 12/9/2017 10:38 AM, agrays...@gmail.com <javascript:> wrote: > > But you don't know which part of the shift of the H is due to > > cosmological expansion, so that's why the method I described seems > > necessary. You must estimate how much is due to expansion alone via > > distance knowledge and Hubble's law, and then calculate the difference > > between the total H red shift and what expansion would give in the > > absence of Doppler, to get the actual Doppler shift. AG > > It's all Doppler shift, you are apparently worrying about peculiar > velocities of galaxies as would be measured by astronmers in the galaxy > relative to the CMB. These may be of interest but they are at the level > of a small noise on top of the Doppler due to expansion of the universe. > > Brent >
The relative motions of galaxies is only important for an observer for nearby galaxies. The Andromeda galaxy is actually approaching the Mikly Way, where the two will mash up in about 4 billion years. Most relative motion of galaxies is orbital motion in galaxy clusters that is on the order of a few hundred kilometers per second. This is important for the local group and to some extend the Virgo group, of which the local group is a sort of subgroup. However, here z ~ .01 which is pretty small. For larger z galaxies or clusters the relative motions of galaxies is negligible. LC -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
