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?

  • $\begingroup$ You have asked lots of similar questions on Physics SE. What is it about en.wikipedia.org/wiki/Radar_astronomy (that you have been referred to) that is unclear? $\endgroup$ – ProfRob Aug 9 '16 at 22:12
  • $\begingroup$ Also, could you clarify the question? Is this about radar, or about seeing a radio shadow due to the SZ effect? Note: The wikipedia explanation is somewhat lacking in this context. $\endgroup$ – Alex Aug 11 '16 at 16:34
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    $\begingroup$ 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. $\endgroup$ – James K Dec 21 '16 at 14:46