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https://en.wikipedia.org/wiki/Axial_tilt#Solar_System_bodies gives the axial tilt of all planets with two decimal precision, but how and when were they measured so precisely ?

I guess it's "easy" for Mars, Jupiter and Saturn (thanks to the rings ?) but how was it measured for Venus under its clouds, or Uranus + Neptune that are so far away ?

Links to scientific publications would be appreciated.

Thanks

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  • $\begingroup$ You can identify features in Venus' clouds as well as in the atmospheres of the other planets even with amateur equipment - and track them if you get a long enough sequence. Their rotation axis gives the tilt. $\endgroup$ – planetmaker Feb 10 at 16:40
  • $\begingroup$ With Venus you can also do earth-based radar measurements of the solid surface (or could until Arecibo crashed). And of course everything can be measured in-situ by orbiters. $\endgroup$ – planetmaker Feb 10 at 16:56
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    $\begingroup$ The gas giants have powerful magnetospheres that can be observed by radio astronomy. Though in the case of Uranus, it isn't aligned with the spin axis, hehe: physicsworld.com/a/… . Luckily Uranus also has observable rings. $\endgroup$ – Connor Garcia Feb 10 at 17:54

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