Coordinate transformation from earth to solar

Question

I am building a 3D model of the solar system and need to figure out the position of the pole stars of each planet in order to tilt the planets in the correct direction the correct amount. I've already found the information of the pole star locations, the problem is that these are in earth relative coordinates. For instance the pole star of Mars is Gamma Cygni at RA 20h 22m 13.70184s, Dec +40° 15' 24.0450".

Right Ascension (RA) is hours east from the prime meridian. Declination (Dec) is degrees north (+) or south (-) from the equator. These together define a position on an imaginary celestial sphere on the surface of which one can imagine all the stars?

So how do I go from those coordinates to a vector that defines the position of the star somewhere far far away on the celestial sphere?

I am using ThreeJS. This question points to a partial solution in terms of defining an origin for a sphere, or at least its texture.

EDIT I've posted the same question to physics.stackexchange.com here

Answer 1

I got this answer on physics.stackexchange.com

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Welcome to the confusing world of coordinate systems used in astronomy!

The two coordinate systems relevant to your problem are the International Celestial Reference System (ICRS), and the ecliptic coordinate system. The first one is really well-defined, the latter is "simply" derived from that.

Put simply, the ICRS is based on extending the Earth's equatorial plane out to infinity. The system places the X-axis in line with the Sun-equinox line. the Z-axis points to Earth's North pole, and Y completes the right-handed system.

Needless to say, this system is not the most natural choice when viewing the Solar system from afar. A more natural choice there is the ecliptic coordinate system. This system follows the same definition as the ICRS, except that the ecliptic (roughly the plane the Earth's orbit lies in) is extended out to infinity, not the equatorial plane.

It's fairly straightforward to convert ecliptic coordinates to equatorial coordinates and back. Don't forget to convert angular distances (RA, dec) to Euclidian coordinates, with the distance to the pole star equal to 1 (this facilitates computations and provides a nice check).

Rody Oldenhuis