How do Cosmic Microwave Background missions/telescopes measure CMB temperatures? I understand that CMB has Planck's spectrum. So I was thinking one strategy could be to measure the spectral radiance corresponding to different frequencies coming from a certain direction and then compared these data points with theoretical Planck's law. Is this technique practically feasible?
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3$\begingroup$ Yes, that is exactly what is being done. $\endgroup$– AtmosphericPrisonEscapeApr 26 '20 at 11:47
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$\begingroup$ @AtmosphericPrisonEscape, this could be a source: astro.uni-bonn.de/~kbasu/ObsCosmo/Slides2019/CMB_Part1.pdf (slide 19) $\endgroup$– Awais MirzaApr 27 '20 at 3:01
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That is what is done. This is shown in an old xkcd comic https://xkcd.com/54/
The curve shows the distribution of frequencies in the CMB, and by using the marked value of the maximum you can determine the value of T, the apparent (red-shifted) temperature of the CMB
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$\begingroup$ Source: astro.uni-bonn.de/~kbasu/ObsCosmo/Slides2019/CMB_Part1.pdf (slide 19) $\endgroup$ Apr 27 '20 at 2:58
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$\begingroup$ In Physics SE we can ask questions about XKCD's, in Biology SE not so much. However in Astronomy KXCD's can serve as answers! $\endgroup$– uhohApr 28 '20 at 23:10