How sure can we be of the distances in the solar system?

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And directly related to that: How can we be sure of the speed of light? I've been searching for a good answer as to how we measure the SOL and am yet to have someone give me a solid explaination. Today we shine a laser at a mirror on the moon and time how long it takes to get back. What it sounds like to me is: we use the SOL to measure a distance that we use to measure the SOL.

I've also heard that we have a device that measures how many times light bounces between 2 points within 1 meter. If im not mistaken thats 3x10^8 times in 1 sec.

This to me seems like a pretty important thing to know considering our science is pretty well based on the SOL.
 

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D H
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Physicists have been measuring the speed of light with ever-improving accuracy for quite some time now. Interferometry-based experiments provided incredibly accurate measurements. Nowadays, with the speed of light defined as 299,792,458 m/s (exactly), those same interferometry-based experiments provide ever-refined means to establish a baseline for the meter.
 
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Chronos
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Having landed probes on, or put them in orbit around, most of the planets in the solar system is compelling evidence our distance estimates are pretty accurate.
 

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