<p>That is what is done.  This is shown in an old xkcd comic <a href="https://xkcd.com/54/" rel="nofollow noreferrer">https://xkcd.com/54/</a></p>

<p><a href="https://i.sstatic.net/dOuOt.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/dOuOt.png" alt="enter image description here"></a></p>

<p>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</p>

CC BY-SA 4.0
2020-04-27T02:58:01.233Z
Source: https://astro.uni-bonn.de/~kbasu/ObsCosmo/Slides2019/CMB_Part1.pdf (slide 19)
Awais Mirza
CC BY-SA 4.0
2020-04-28T23:10:22.780Z
In Physics SE we can [ask questions](https://physics.stackexchange.com/q/420542/83380) about XKCD's, in Biology SE [not so much](https://biology.stackexchange.com/q/93026/27918). However in Astronomy KXCD's can serve as answers!
uhoh
CC BY-SA 4.0
2020-04-26T16:35:16.023Z
2020-04-26T16:35:16.023Z
James K
<p>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 <a href="https://en.wikipedia.org/wiki/Radiance" rel="nofollow noreferrer">spectral radiance</a> corresponding to different frequencies coming from a certain direction and then compared these data points with theoretical <a href="https://en.wikipedia.org/wiki/Planck%27s_law" rel="nofollow noreferrer">Planck's law</a>. Is this technique practically feasible? </p>

CC BY-SA 4.0
2020-04-26T11:47:49.733Z
Yes, that is exactly what is being done.
AtmosphericPrisonEscape
CC BY-SA 4.0
2020-04-27T03:01:02.170Z
@AtmosphericPrisonEscape, this could be a source: https://astro.uni-bonn.de/~kbasu/ObsCosmo/Slides2019/CMB_Part1.pdf (slide 19)
Awais Mirza
<observational-astronomy><cosmic-microwave-background><radio-telescope><black-body>
How is Cosmic Microwave Background's temperature measured?
Awais Mirza
# How is Cosmic Microwave Background's temperature measured?

(Asked by: username_0 on 2020-04-26)

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](https://en.wikipedia.org/wiki/Radiance) corresponding to different frequencies coming from a certain direction and then compared these data points with theoretical [Planck's law](https://en.wikipedia.org/wiki/Planck%27s_law). Is this technique practically feasible?

**Tags:** observational-astronomy, cosmic-microwave-background, radio-telescope, black-body

> **Comments:**
> **username_1**: Yes, that is exactly what is being done.  
> **username_0**: @username_1, this could be a source: https://astro.uni-bonn.de/~kbasu/ObsCosmo/Slides2019/CMB_Part1.pdf (slide 19)  

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## 1 answers

### Answer by username_2 on 2020-04-26. Score: 3 | Accepted answer

That is what is done. This is shown in an old xkcd comic <https://xkcd.com/54/>

[![enter image description here](https://i.sstatic.net/dOuOt.png)](https://i.sstatic.net/dOuOt.png)

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

> **Comments:**
> **username_0**: Source: https://astro.uni-bonn.de/~kbasu/ObsCosmo/Slides2019/CMB_Part1.pdf (slide 19)  
> **username_3**: In Physics SE we can [ask questions](https://physics.stackexchange.com/q/420542/83380) about XKCD's, in Biology SE [not so much](https://biology.stackexchange.com/q/93026/27918). However in Astronomy KXCD's can serve as answers!  

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