[Kstars-devel] problem with precession

[Jason Harris]

Hello,

I've run across a problem: when I set the date to 1 Jan 2000, the 
coordinates of stars are NOT equal to their catalog J2000 coordinates.  

As a test, I entered the J2000 cordinates for Sirius into the 
astrocalculator "apparent coordinates" module, and set the target date 
to 1 Jan 2000.  I get the same wrong coordinates as in the skymap:

Sirius catalog coordinates:   06 45 09.25, -16 42 47.3
Coordinates on 1 Jan 2000 in KStars: 06 45 09.94, -16 42 52.76

However, the same experiment in the "Precession" calc module gives the 
right answer.  So the problem is in one of the other corrections 
(aberration or nutation).

Adding some debugs to the code, I found that the functions KSNumbers::
dObliq() and KSNumbers::dEcLong() are non-zero when jd==J2000.  I'm 
pretty sure they should both be zero in this case.

Looking at how deltaObliquity and deltaEcLong are set in ksnumbers.cpp, 
it isn't obvious what the problem is.  I'll try to figure it out this 
weekend, but feel free to beat me to it. :)

Jason 

-- 
KStars: A KDE Planetarium
http://edu.kde.org/kstars