Fundamental plane

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (November 2006)

The fundamental plane in a spherical coordinate system is a plane which divides the sphere into two hemispheres. The latitude of a point is then the angle between the fundamental plane and the line joining the point to the centre of the sphere.

For a geographic coordinate system of the Earth, the fundamental plane is the equator. Celestial coordinate systems have varying fundamental planes:

• the equatorial coordinate system uses the celestial equator;
• the ecliptic coordinate system uses the ecliptic;
• the galactic coordinate system uses the Milky Way; and
• the horizontal coordinate system uses the observer's horizon.