On Saturday, December 9, 2017 at 9:22:35 PM UTC, Lawrence Crowell wrote: > > On Saturday, December 9, 2017 at 2:38:49 PM UTC-6, Brent wrote: >> >> >> >> On 12/9/2017 10:38 AM, [email protected] 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. >
I know. I was just trying to distinguish the two forms of Doppler and how they can be individually measured and/or calculated. Yes, it's all Doppler as Brent says. AG > > 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 [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
