Fundamental plane (spherical coordinates)
The fundamental plane in a spherical coordinate system is a plane of reference that divides the sphere into two hemispheres. The geocentric latitude of a point is then the angle between the fundamental plane and the line joining the point to the centre of the sphere.[1]
For the concept in extragalactic astronomy, see Fundamental plane (elliptical galaxies).
For a geographic coordinate system of the Earth, the fundamental plane is the Equator.
Astronomical coordinate systems have varying fundamental planes:[2]