• Pablo de Vicente's avatar
    Fixed a bug first pointed out by Mikhail Zotov in a private communication, · 152179b5
    Pablo de Vicente authored
    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
    152179b5
modcalcprec.cpp 10.2 KB