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.
- The horizontal coordinate system uses the observer's horizon.
- The Besselian coordinate system uses Earth's terminator (day/night boundary). This is a Cartesian coordinate system (x, y, z).
- The equatorial coordinate system uses the celestial equator.
- The ecliptic coordinate system uses the ecliptic.
- The galactic coordinate system uses the Milky Way's galactic equator.
- Rogers, Lucy (2008), It's ONLY Rocket Science: An Introduction in Plain English, Springer, p. 136, ISBN 9780387753782.
- Newcomb, Simon (1906). A Compendium of Spherical Astronomy with Its Applications to the Determination and Reduction of Positions of the Fixed Stars. Macmillan. p. 92..