How to calculate the orientation of planets at current epoch For an application I am working on I am creating a simulation of the solar system. In this simulation, a user needs to be able to 'move' to any position on any planet, and have the sky be accurately simulated around him.

Using the examples &amp; calculations provided at http://stjarnhimlen.se/comp/ppcomp.html and the data provided at https://ssd.jpl.nasa.gov/txt/aprx_pos_planets.pdf I am able to compute the POSITIONS of the planets at any date, however, what I am still looking for is the ORIENTATION of these planets at that position (i.e. which way is Long 0 Lat 0 pointing, and which way is Long 0 Lat 90 pointing (with respect to the vernal equinox)). I need this orientation in order to figure out what the rotation (quaternion) of this planet needs to be..

I have been looking around, but have so far not been able to find a source for any kind of information like this. The closest I've found was https://en.wikipedia.org/wiki/Poles_of_astronomical_bodies , but that only gives me an up-vector, not a 'forward' (and is for J2000, not the current Epoch).

Can anyone be of assistance?
The IAU WGCCRE (Working Group on Cartographic Coordinates and Rotational Elements) seem to be the authorities on this.
Table 1 in their 2015 report gives the following information for the major planets:

α0, δ0 are the ICRF right ascension and declination of the planet's north pole. If the planet's axial precession is known, these are expressed in terms of T, the number of Julian centuries since epoch J2000.0.

W is the rotation angle eastward from reference point Q to the planet's prime meridian at time d, where Q is the intersection of the planet's equator and the ICRF equator at RA α0 + 90°, Dec 0°, and d is the number of days since epoch J2000.0.


They define a planet's north pole as the one pointing north of the solar system's invariable plane.
This means that W decreases with time for Venus and Uranus.
Their figure 1 appears to indicate Q's RA as 90° - α0, in conflict with the text. I believe the text is correct.
When you are ready to validate your calculations, the S&amp;T Mars Profiler shows which side of Mars faces Earth at a given time.