Christian Froeschlin wrote:
[...]
> Did you test it against your original star chart? The only
> test I did was to see if the vernal point would rise due east
> at spring equinox 6am so I hoped it was correct. But I did a
> lot of trial and error with the signs: mixing three celestial
> coordinate systems with POV-Ray's left-handed one caused a
> bit of brain overload at times ;)

Thanks for the cleanup tips.  I've only had time to do a quick test, but only
one small change in the rotation calculations was needed for everything to line
up a sky_sphere properly for my test date and time.

Toward the bottom, the line...

  #declare A_LOCAL = HourAngle(YEAR,MONTH,DAY,HOUR,MIN,LONG,LAT,LONG);

....is now...

  #declare A_LOCAL = HourAngle(YEAR,MONTH,DAY,HOUR,MIN,LSTM,LAT,LONG);

....with LSTM set as Lstm is in sunpos.

I'll finish recasting your code as a macro and post it as time permits.

Also, although I'm using this for a current fairly small animation, my primary
interest is for a long-term POV-Ray project that could be described as a
5,000-year time-lapse sequence, so I'll be looking into precession corrections
later.

Again, I thank you for this stellar (pun intended) example of the wonderful
support within the POV-Ray community.

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