I can find axial tilt of planets easily, but that doesn't specify the direction of that tilt, i.e. planet's rotation axis may be anywhere in circle defined on a sphere by axial tilt value. And I can't google for obliquity direction as it only gives me obliquity value, not it's direction. Even NASA's HORIZONS only gives obliquity value. I expect there should be another angle, either from main body equinox, Earth's equinox, ascending node or maybe periapsis, that with axial tilt and orbital elements would define direction of planet's rotation axis. I know that the rotation axis precesses, but that takes thousands of years, and compared to time from J2000 it's practically neglectable (or at least it's easier to find precession rate and make a correction for it, knowing some starting value).


1 Answer 1



PM 2Ring posted the answer in the above comment. The direction of each planet's rotational axis in RA/Dec can be found in the table here: en.wikipedia.org/wiki/Axial_tilt#Solar_System_bodies.


Astronomers have defined a coordinate system on the Celestial sphere, with z-axis coincident with Earth's North Pole, and x-axis pointed to the First Point of Aries (aligned with the vernal equinox). Two angles define a point on the celestial sphere: right ascension and declination are analogous to longitude and latitude respectively as shown from this wikipedia plot.

enter image description here


Uranus' North Pole direction had RA/Dec of 257.31, −15.18 degrees according to the wikipedia table from the IAU at 0 January 2010, 0h TT, putting it in the hydra constellation (graphic from Wikipedia) at that time:

enter image description here

  • $\begingroup$ Then wiki values defined in Earth's equatorial plane. Is there same values for ecliptic plane? Or how to determine Earth's equatorial plane in relation to ecliptic plane? $\endgroup$
    – Aberro
    Aug 26, 2021 at 14:55
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    $\begingroup$ At the vernal equinox, subtract 23.44 degrees from the Declination to get the coordinates in the ecliptic plane as shown in the first plot above. $\endgroup$
    – Connor Garcia
    Aug 26, 2021 at 15:41

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