Triplet (

*ρ*,*θ*,*φ*) of numbers associated with the position of a point P in a three‑dimensional space in a spherical locating system. The numbers*ρ*,*θ*and*φ*are the distance from P to the centre of the sphere and the angles of rotation with the*x*‑axis and the*z*‑axis.In this system,

*ρ*represents the distance from the point P to the centre O of the reference sphere; the angle*θ*is the rotation angle of the*x*-axis toward the orthogonal projection OP’ of the radius OP on the plane*xy*(represented in colour in the figure);*φ*is the rotation angle of the*z*‑axis on the radius OP.A spherical coordinate system is a synthesis between the Cartesian coordinate system in a three-dimensional space and a polar coordinate system.

### Examples

- The spherical coordinate system is used in astrometry to study the distance and the movement of stars in relation to the solar system or in relation to one another.
- Earth’s coordinate system is not, properly speaking, a spherical coordinate system because the distance from one point on the globe to the centre of the Earth is not involved.