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From: Tom Roberts on 24 Feb 2010 01:21
Yimin Rong wrote:
> Consider an observer moving at an extremely high velocity relative to
> the CMBR (e.g. v = 0.999999c).
>
> In the direction of travel, one would expect the CMBR to be blue
> shifted into infrared and visible. Would there be a difference in the
> intensity of the radiation in the blue shifted direction vs. the red
> shifted direction vs. at rest?

Yes, of course. Motion relative to its dipole=0 frame induces both frequency
(energy) redshift/blueshift and a corresponding decrease/increase in intensity
(where by intensity I mean Watt/cm^2).


> I found this: http://en.wikipedia.org/wiki/File:Firas_spectrum.jpg.
> The intensity is given in ergs / (centimeter squared x steradian x
> second x inverse centimeter). Can that be converted to something like
> W/m^2?

Sure. Convert ergs to joules, integrate over wavelength (in cm), and integrate
over 2pi steradians. That will give watts/cm^2 for all radiation impinging on
one side of a flat detector. Note the data should first be corrected to
correspond to the dipole=0 frame; but that's a rather small effect, and may not
be visible at the scale of the figure. The integral over angles (steradians)
should take into account the anisotropies, but that is definitely too small to
be visible in the figure.

For a detector moving relative to the dipole=0 frame the integral over angles
(steradians) will be tricky.


Tom Roberts
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