Supergalactic coordinate system
Supergalactic coordinates are
coordinates in a
spherical coordinate system which was designed to have its
equator aligned with the
supergalactic plane, a major structure in the local universe formed by the preferential distribution of nearby
galaxy clusters (such as the
Virgo cluster, the
Great Attractor and the
Pisces-Perseus supercluster) towards a (two-dimensional)
plane. The supergalactic plane was recognized by
Gérard de Vaucouleurs in 1953 from the
Shapley-Ames catalogue, although a flattened distribution of
nebulae had been noted by
William Herschel over 200 years earlier.
By convention, supergalactic latitude and supergalactic longitude are usually denoted by SGB and SGL, respectively, by analogy to
b and
l conventionally used for
galactic coordinates. The zero point for supergalactic longitude is defined by the intersection of this plane with the galactic plane.
*The north supergalactic pole (SGB=90°) lies at galactic coordinates (
l=47.37°,
b=+6.32°). In the
equatorial coordinate system (
epoch J2000), this is approximately (
RA=18.9 h,
Dec=+15.7°).
*The zero point (SGB=0°, SGL=0°) lies at (
l=137.37°,
b=0°). In J2000 equatorial coordinates, this is approximately (2.82 h, +59.5°).
*
Coordinate system*
Precise definition by Lahav et al 2000, MNRAS, 312, 166
