Equatorial coordinates (Right ascension and Declination) are given for two equinoxes 1950 (Besselian coordinates al1950, de1950) and 2000 (Julian coordinates al2000, de2000). Most of published coordinates are B1950 coordinates. Conversion to J2000 has been made according to the "Merits Standards" published in the U.S. Naval Observatory Circular (1983). For computer use, coordinates are expressed as decimal values (hours to 0.00001 and degrees to 0.0001 for Right Ascension and Declination, respectively). The standard deviation of coordinates is generally not known. Thus we are using a flag ipad to tell if the standard deviation is smaller than 10 arcsec or not. We collected systematically accurate coordinates in literature (see Paturel et al. 1989). Recently, we added accurate coordinates directly obtained from images stored in LEDA (Paturel et al. 1996) and from COSMOS database (Rousseau et al. 1996). Among the 100872 galaxies 69165 have accurate coordinates (69 percent).
Galactic coordinates l2, b2 are calculated (in degrees to 
)
from al1950 and de1950 using the coordinates of the galactic pole
al1950(pole) = 12.81667 de1950(pole) = 27.4000 and
the coordinates of the origin al1950(origin) = 17.70667 de1950
(origin) = -28.9167
according to Blaauw et al. (1960). These galactic coordinates are
used to estimate the galactic extinction ag converted to Burstein-Heiles
system (Burstein & Heiles 1984) from the relationship given in the
Second Reference Catalog (de Vaucouleurs et al. 1976;
p32, rel. 22; hereafter RC2). In fact, for galactic latitude 
the
difference between both systems is negligibly small (except for the zero
point difference of 0.20 mag due to the fact that Burstein-Heiles give
no absorption at the galactic pole).
In Fig. 1 (click here) the difference between ag from RC2 and from
Burstein-Heiles is plotted vs. the galactic latitude.
Figure 1: Difference of galactic extinction from RC2 and
Burstein-Heiles vs. the absolute value of the galactic latitude
The conversion from RC2- to BH-system is the following:
if 
:
and if 
:
The galactic extinction is higher than the one predicted by RC2 formula
for low galactic latitude (
). The adopted galactic
extinction is ag=ag(BH)+0.20, where ag(BH) is calculated from Rel. 1 and
Rel. 2.
Supergalactic coordinates sgl, sgb are calculated (in degrees to 
)
from l2, b2 using the coordinates of the supergalactic pole
l2(pole) = 47.37 deg b2(pole) = 6.32 deg and the coordinates of the origin
l2(origin) = 137.37 deg; b2(origin) = 0 deg according to
de Vaucouleurs et al. (1976).