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.


  • $\begingroup$ 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. $\endgroup$ Feb 10, 2021 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. $\endgroup$ Feb 10, 2021 at 16:56
  • 3
    $\begingroup$ 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, 2021 at 17:54
  • $\begingroup$ See: astronomy.stackexchange.com/questions/11182/… $\endgroup$ Jul 9, 2021 at 5:18
  • $\begingroup$ The values are available with greater than two decimals of precision on these sub-pages: nssdc.gsfc.nasa.gov/planetary/planetfact.html - found by following the reference on Wikipedia. $\endgroup$
    – Rob
    Aug 14, 2021 at 0:31


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