Editing Spherical coordinate system (section)

=== In astronomy ===
A series of [[astronomical coordinate systems]] are used to measure the elevation angle from several [[Fundamental plane (spherical coordinates)|fundamental planes]]. These reference planes include: 
the observer's [[Horizontal coordinate system|horizon]], the [[Galactic coordinate system|galactic equator]] (defined by the rotation of the [[Milky Way]]), the [[celestial equator]] (defined by Earth's rotation), the plane of the [[Ecliptic coordinate system|ecliptic]] (defined by Earth's orbit around the [[Sun]]), and the plane of the earth [[terminator (solar)|terminator]] (normal to the instantaneous direction to the [[Sun]]).