||A spherical coordinate system in which the equator is the supergalactic plane. Supergalactic
longitude, SGL, is measured counterclockwise from direction l = 137.37 deg, b = 0
deg (between 0 and 360 deg). The zero point for supergalactic longitude is defined
by the intersection of this plane with the Galactic plane. In the equatorial coordinate
system (J2000) this is approximately 2.82 h, +59.5 deg. Supergalactic latitude, SGB,
is measured from the supergalactic plane, positive northward and negative southward.
The North Supergalactic Pole (SGB=90 deg) lies at galactic coordinates l = 47.37 deg,
b = +6.32 degrees, corresponding to the equatorial coordinate system (J2000) 18.9
h, +15.7 deg.