who noticed that precession between B1950 to J2000 as done by KStars does not
coincide with the results given by SIMBAD (http://simbad.u-strasbg.fr/sim-fidl.pl).  M. Zotov has not opened yet a bug in bugs.kde.org, so I have no bug
number to refer to in this commit.

  The bug comes from the fact that conversion between coordinates in B1950
to J2000 (and viceversa) involves changing from (old) catalog FK4 to FK5,
and a simple precesion, as done by KStars is not enough.

To fix this bug I have used the following reference:
Smith, C. A.; Kaplan, G. H.; Hughes, J. A.; Seidelmann, P. K.; Yallop,
B. D.; Hohenkerk, C. Y.
Astronomical Journal, vol. 97, Jan. 1989, p. 265-279

The conversion between the FK4 catalog and the FK5 catalog requires 4 steps:
 - Drop E-Terms in B1950 coordinates. In the past, the mean places of
   stars published in the FK4 catalog included the contribution to the
   aberration due to the ellipticity of the orbit of the Earth. These terms,
   known as E-terms were almost constant, and in the newer FK5 catalog they
   are not included.
 - Precess from B1950 to 1984, January 1st, at 0h, using the parameters
   given by the Astronomische Rechen-Institut.
 - Apply the zero-point correction to the right ascensions to correct for the
   equinox error of the FK4. This is done for 1984, Jan 1st, at 0h.
 - Precess from 1984 Jan 1st at 0h, to J2000 using the new precessional
   parameters.

   This bug may seem not important since KStars produces a result which is
almost correct, but since the conversion between B1950 and J2000 is done
very frequently among astronomers it needs to be corrected. This bug affects
the precessional module and the galactic/equatorial conversion module. This
fix ONLY applies to the first module, although now it is straightforward to
correct the second module. I will do this later.

  Since Stephan Kulow only accepts big bug fixes in the KDE 3.2 deep freeze
period in order to ensure a fast stability of the first relase, I commit
these fixes only to the KDE 3.1.4 branch, even knowing there may be no ç
KDE 3.1.5 release in the future. As soon as the KDE 3.2 branch is opened
for small bug fixes I will port this fix.

CCMAIL: kstars-devel@kde.org

svn path=/branches/KDE_3_1_BRANCH/kdeedu/kstars/; revision=269012