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<a href=" Hi Burkhard & All, Thanks Burkhard. You have answered my question. Not really an argument; just need for clarification. The red shift I now understand is measured not by their being less light of shorter wavelength but by displacement of spectral lines, presumably to a longer than normal wavelength. So the spectral lines of e.g. hydrogen in some state would all be shifted to a somewhat longer wavelength. But I do have problems with the concept of everything having started with an explosive expansion of some kernel of infinite density; just after God said "Let there be light"; aka big bang. Dave On 2019-04-07 12:13 p.m., Burkhard Plache wrote: > 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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