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Index of Subjects Hi Dave, your last question makes the correct observation that of all the light emitted by a distant object, the shorter wavelength light will be preferentially scattered away, leaving more of the original red light than blue light arriving at our doorsteps. Your implied, though not stated, assumption seems to be that redshift is measured by 'relative amounts of light' or 'the light looking more red'. - However, redshift is measured by looking at spectral lines, which are not modified by Rayleigh scattering. - Could you clearly state what your argument is? Thanks, Burkhard On Sun, Apr 7, 2019 at 10:53 AM David Webster <dwebster@glinx.com> wrote: > > > On 2019-04-07 8:45 a.m., Burkhard Plache wrote: > > Hi David, > > to correct a common misrepresentation: The cosmological red shift of > > light is not due to the source moving away but due to the space > > expanding. Two very different phenomena. > > Also, Rayleigh scattering is not changing the wavelength of the > > scattered light, hence is not contributing to redshift. > > Burkhard > > > > On Sun, Apr 7, 2019 at 8:17 AM David Webster <dwebster@glinx.com> wrote: > >> Hi Burkhard, > > Thanks. It seems to me that we are getting tangled up in semantics. > > If space expands then it makes objects appear to be moving away. > > And, indeed, scattering does not destroy shorter wavelengths but it > does deflect them so they are partially or entirely culled from those > waves which are moving from source to observer. Thus, at the local > level; blue skies, white clouds, red sunsets and that green flash which > one sometimes sees from the cockpit when landing and facing west near > sunset. > > The above are all effects of our atmosphere. But there is ample > evidence of cosmic dust, ranging from particles to atoms, so one would > expect scattering of shorter wavelengths throughout space to increase > with distance between observer and source; greater opportunity for > scattering. > > So rephrasing my question in current jargon, are red shifts of > light due to expansion of space, distinct from red shifts which might be > due to Rayleigh scattering whereby shorter wavelengths from a source are > less likely to reach an observer ? > > Or more directly, why is the observed increase in red shift with > distance between source and observer attributed to an expansion of > space as opposed to greater opportunity for scattering of shorter > wavelengths of light as this distance increases ? > > Dave > > > > > >> Dear All, but especially astrophysics experts, > >> > >> Is the red shift of light, which would be due to the source moving > >> away at great speed, intrinsically unlike the red shift due to Rayleigh > >> scattering (which selectively scatters shorter wavelengths; 1/[length to > >> the fourth power]) ? > >> > >> With ample dust in space, ranging from particles to atoms, one > >> would expect the red shift due to scattering to also be a function of > >> distance to source. > >> > >> Dave Webster, Kentville > >>
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