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The supergalactic coordinate system is a spherical coordinate system used for directions in the celestial sphere, fixed to the supergalactic plane, and the line intersecting that plane with the galactic plane. The supergalactic plane is a determination of an apparent plane that nearby galaxy clusters neighbor, including the Virgo Cluster, the Great Attractor and the Perseus-Pisces Supercluster. The system's spherical elements are supergalactic longitude (SGL or l), and supergalactic latitude (SGB or b).
| defining directions | supergalactic | galactic | equatorial (approx.) |
| "supergalactic north pole" | +90° | l=47.37° b=+6.32° | J185501+154232.2 |
| "supergalactic zero point" | 0° 0° | l=137.37° b=0° | J024914.4+593141.8 |
The above galactic coordinates are exact by definition. Gérard de Vaucouleurs devised the system based upon his determination of a supergalactic plane, including them in his 1976 catalog of galaxies, Second reference catalogue of bright galaxies.