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Дата изменения: Mon Dec 23 18:23:59 2013
Дата индексирования: Fri Feb 28 18:24:27 2014
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HyperLEDA documentation: parameter: celpos

Celestial position: celpos

The position of the objects on the sky were generally measured to a precision between 1 and 4 arcsec. The homogenized position is computed by averaging all measurements belonging to the best available quality class for the object (field 'flag' in the astrometric compilation).

The original measurements are now accessible from the current interface.
For the stars, the position is always at epoch 2000, whatever J2000 or B1950 coordinates are printed. This is because proper motions are not stored in the database. For a correct astrometry of stars, en advice to use Simbad.

The celestial position is given as coordinates in 4 different systems:
SystemDescription
B1950Equatorial coordinates, Besselian, Equinox 1950.0, Epoch 2000.0
J2000Equatorial coordinates, Julian, Equinox 2000.0, Epoch 2000.0
G Galactic coordinates in the reference frame called "new" system, adopted by IAU in 1958. Galactic pole at B124900.0+272400, node at ra=282.25,l=33 deg (inclination 62.6 deg). The B1950 north celestial pole is at l=123, b=27.4 deg.
SGSupergalactic coordinates. Supergalactic equator is conceptually defined by the plane of the local (Virgo-Hydra-Centaurus) supercluster, and the origin of supergalactic longitude is at the intersection of the supergalactic and galactic planes. See the definition in RC2 (de Vaucouleurs et al. 1976) and RC3 (de Vaucouleurs et al. 1991): North SG pole at l=47.37 deg, b=6.32 deg. Node at l=137.37, sgl=0 (inclination 83.68 deg).
Note: The position of the SG node reported in RC2 (137.29 deg) differs from RC3 (137.37 deg; see page 12, the difference is mentioned but not commented).
The precision of the position is coded in the flag f_astrom as:
f_astrom
 definition
-1
 precision about 0.1 arcsec
0
 1 arcsec
1
 10 arcsec
2
 100 arcsec (1 arcmin)
3
 1000 arcsec (10 arcmin)
The adopted precision flag is the most precise of those available in the astrometric compilation.

The coordinates are printed in a compact format, with no embedded blanks, which is recognized in input as well (but input may be given in free format also).

In SQL search constraints may be put on the following parameters
ParameterDescription
al2000Right ascension J2000
de2000Declination J2000
al1950Right ascension B1950
de1950Declination B1950
l2Galactic longitude
b2Galactic latitude
sglSuper Galactic longitude
sgbSuper Galactic latitude
f_astromPrecision flag on the celestial position

The determination of the astromery in HyperLeda is presented in the following articles:

HyperLeda Questions: prugniel@obs.univ-lyon1.fr