In the 18th century, the distance to the Sun was measured using the transits of Venus. Nowadays, the timing of radar pulses is used to measure the distance of things in our solar system. What instruments are used to perform these measurement? What do they look like (bonus points for pictures)? Are there observatories with "radar guns" dedicated to measuring the distance of the Sun?
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They look like radio telescopes, because that is what they are.
Some radio telescopes have been outfitted to transmit rather than receive, requiring using a different radio telescope to receive the reflected signal. Other radio telescopes have been outfitted to transmit as well as receive in a pulsed manner. These can be used for radar astronomy without the help of a separate transmitter.
answered Oct 7, 2020 at 15:11
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1$\begingroup$ ...but not at the Sun, right? "Are there observatories with "radar guns" dedicated to measuring the distance of the Sun?" Reminds me of In the novel The Three-Body Problem, does the Sun's amplification of radio transmissions have a scientific basis? :-) $\endgroup$– uhohOct 7, 2020 at 15:28
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1$\begingroup$ @uhoh - "A serious long-term attempt to study the corona using radar was made between 1961 and 1969, but it was unsuccessful because the characteristics of the radar echo could not be explained. In retrospect it was not possible to adequately model the radar echoes because we did not know enough about the corona at that time. Further observations became impossible as radar astronomy evolved and the technique has been almost forgotten." $\endgroup$ Oct 7, 2020 at 16:44
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1$\begingroup$ Reference for the above: Coles, William A. "Solar radar." Solar and Space Weather Radiophysics. Springer, Dordrecht, 2004. 335-353. So it has been done, but apparently it's not all that useful. (The referenced article has only been cited seven times since it was published in 2004.) $\endgroup$ Oct 7, 2020 at 16:45