On Fri, Dec 08, 2017 at 08:03:48PM -0800, agrayson2...@gmail.com wrote: > > > On Saturday, December 9, 2017 at 3:53:28 AM UTC, agrays...@gmail.com wrote: > > > > > > > > On Saturday, December 9, 2017 at 2:40:12 AM UTC, Russell Standish wrote: > >> > >> On Fri, Dec 08, 2017 at 12:59:16PM -0800, agrays...@gmail.com wrote: > >> > > >> > > >> > On Friday, December 8, 2017 at 3:04:42 PM UTC, agrays...@gmail.com > >> wrote: > >> > > > >> > > How is it distinguished from red and possibly blue shifting due to > >> > > relative motion of distant galaxies? TIA, AG > >> > > > >> > > >> > I meant to ask how one distinguishes the Doppler shift (red or blue) > >> from > >> > the Cosmological shift (red) for distant galaxies. TIA, AG > >> > > >> > >> The answer is you don't. However, for those galaxies we have an > >> independent measure of distance (via so-called standard candles), the > >> Hubble law holds (velocity away from us as measured by Doppler shift > >> is on average proportional to the distance away). It is a reasonable > >> extrapolation that the Hubble law holds for the entire visible > >> universe. > >> > > > > I think what you're implying but not expressly stating is that if one > > measures the red shift and knows the distance, one then apply estimate the > > departure of s ;awred shift from what Hubble's law implies, one can > > estimate the Doppler shift. AG > > > > > > > *Ignore above statement; accidentally posted.I think what you're implying > but not expressly stating is that if one MEASURES the TOTAL red shift and > knows the distance, one can use the known distance and Hubble's law to > calculate what the Cosmological red shift SHOULD be, and from that > calculation and the DIFFERENCE with the measured red shift, one can > estimate the Doppler shift. AG * >
The Doppler shift is known, because (eg) hydrogen molecules radiate at a particular wavelength around 21cm, and when we observe a certain galaxy, the light shows that same hydrogen radiation band, but at (say) 25cm, then it is redshifted. The velocity of the galaxy (which is away from us in this case) can be computed by the Doppler formula. When the distance is known (eg because a supernova has exploded in that galaxy of known brightness - the "standard candle"), then one can plot distance versus velocity. As general rule, these lie on a line (ie are highly correlated) - that line is known as the Hubble law. -- ---------------------------------------------------------------------------- Dr Russell Standish Phone 0425 253119 (mobile) Principal, High Performance Coders Visiting Senior Research Fellow hpco...@hpcoders.com.au Economics, Kingston University http://www.hpcoders.com.au ---------------------------------------------------------------------------- -- 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.
