<p>I do not have much knowledge about radio astronomy. I know that astronomers know an objects' shape by measuring the reflected photons that reach radiotelescopes, but can they measure also the absorbed ones for the same purpose?</p>

CC BY-SA 3.0
2016-08-09T22:12:40.760Z
You have asked lots of similar questions on Physics SE. What is it about https://en.wikipedia.org/wiki/Radar_astronomy (that you have been referred to) that is unclear?
ProfRob
CC BY-SA 3.0
2016-08-11T16:34:52.993Z
Also, could you clarify the question? Is this about radar, or about seeing a [radio shadow](http://www.astro.yale.edu/~lds4/Research_files/droppedImage.jpg) due to the [SZ effect](https://en.wikipedia.org/wiki/Sunyaev%E2%80%93Zel%27dovich_effect)? Note: The wikipedia explanation is somewhat lacking in this context.
Alex
CC BY-SA 3.0
2016-12-21T14:46:48.250Z
This seems very unclear. My first thought was "If the photon is absorbed, then it can't be measured"... but that seems too obvious. Please clarify.
James K
<planet><radio-astronomy><photons>
Do astronomers measure radio waves absorption to know the shape of a celestial body?
noduagg
# Do astronomers measure radio waves absorption to know the shape of a celestial body?

(Asked by: username_0 on 2016-08-09)

I do not have much knowledge about radio astronomy. I know that astronomers know an objects' shape by measuring the reflected photons that reach radiotelescopes, but can they measure also the absorbed ones for the same purpose?

**Tags:** planet, radio-astronomy, photons
> **Comments:**
> **username_1**: You have asked lots of similar questions on Physics SE. What is it about https://en.wikipedia.org/wiki/Radar_astronomy (that you have been referred to) that is unclear?  
> **username_2**: Also, could you clarify the question? Is this about radar, or about seeing a [radio shadow](http://www.astro.yale.edu/~lds4/Research_files/droppedImage.jpg) due to the [SZ effect](https://en.wikipedia.org/wiki/Sunyaev%E2%80%93Zel%27dovich_effect)? Note: The wikipedia explanation is somewhat lacking in this context.  
> **username_3**: This seems very unclear. My first thought was "If the photon is absorbed, then it can't be measured"... but that seems too obvious. Please clarify.  

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## 0 answers

