So I was stuck on a question involving the transformation of coordinates from geocentric to Mars-centric coordinates. The relative position of Mars and its orbital details are given. I thought that we may neglect the inclination of Mars' orbit with respect to the ecliptic (just have to approximate for this question). Also, inclination of Mars' rotational axis is almost identical to that of Earth. But the problem is, I don't know if the rotational axes are parallel or not, which makes a huge difference here. Have looked up some sources, but didn't get an answer to my question. Would appreciate any help.

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    $\begingroup$ From astronomy.stackexchange.com/a/19378/16685 the north pole of Mars points not toward Polaris, but toward Deneb in Cygnus. $\endgroup$
    – PM 2Ring
    Aug 11, 2023 at 18:50
  • $\begingroup$ @PM2Ring Thanks! Got it. $\endgroup$ Aug 11, 2023 at 19:17
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    $\begingroup$ This might be a bit too much information, but NAIF publishes a text SPICE kernel with the RA/Dec of many solar system bodies. The RA/Dec of Mars' pole is RA: 21.17h, Dec: 52.88deg. So, if you point at that point from Earth, Mars' pole is parallel to your arm. The kernel is plain text: naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/pck00010.tpc $\endgroup$ Aug 12, 2023 at 2:34

1 Answer 1


The polar axis of Mars is not parallel to the polar axis of Earth. The north celestial pole of Earth has a declination of 90°, but the north celestial pole of Mars has a declination of almost 53°.

From Wikipedia, Astronomy on Mars

Celestial poles and ecliptic

The orientation of Mars's axis is such that its north celestial pole is in Cygnus at R.A. 21h 10m 42s Decl. +52° 53.0′ (or more precisely, 317.67669 +52.88378)
The top two stars in the Northern Cross, Sadr and Deneb, point to the north celestial pole of Mars. The pole is about halfway between Deneb and Alpha Cephei, less than 10° from the former, a bit more than the apparent distance between Sadr and Deneb.
Because of its proximity to the pole, Deneb never sets in nearly all of Mars's northern hemisphere. Except in areas close to the equator, Deneb permanently circles the North pole. The orientation of Deneb and Sadr would make a useful clock hand for telling sidereal time.

Here's a view of the celestial north pole on Mars.

Mars north celestial polar region

  • $\begingroup$ So we can take the angle between Earth's axis and Mars' axis as the complement of declination of North Celestial Pole of Mars, right? $\endgroup$ Aug 11, 2023 at 19:30
  • $\begingroup$ @AarushMishra Yes, that's correct. $\endgroup$
    – PM 2Ring
    Aug 11, 2023 at 19:34

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