Supergalactic coordinates are coordinates in a spherical coordinate system which was designed to have its equator aligned with the supergalactic plane, which is the (two-dimensional) plane going through the structure formed by clusters of galaxies close to the Sun. The zero point for supergalactic longitude is defined by the intersection of this plane with the galactic plane.
Definition
The North Supergalactic Pole (SGB=90 deg) lies at galactic coordinates (l=47.37 deg, b=+6.32 deg). In the equatorial coordinate system (J2000) this is approximately (18.9 h, +15.7 deg).
The zero point (SGB=0 deg, SGL =0 deg) lies at (l=137.37 deg, b=0 deg). In the equatorial coordinate system (J2000) this is approximately (2.82 h, +59.5 deg).
