# coordinate system

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The Four Main Coordinate Systems
coordinate system

## coordinate system

() A system, resembling that of latitude and longitude on the Earth, by which the direction of a celestial body or a point in the sky can be specified. The direction is defined and determined by two spherical coordinates, referred to a fundamental great circle lying on the celestial sphere and a point on the fundamental circle (see illustration). One coordinate (a) is the angular distance of the celestial body measured perpendicular to the fundamental circle along an auxiliary great circle passing through the body and the poles of the fundamental circle. The other coordinate (b) is the angular distance measured along the fundamental circle from a selected zero point to the intersection of the auxiliary circle.

There are four main coordinate systems: the equatorial, horizontal, ecliptic, and galactic coordinate systems (see table). They are all centered on the Earth. Transformations can be made from one system to another by means of the relationships between the angles and sides of the relevant spherical triangles. The astronomical triangle, for example, relates equatorial and horizontal coordinates; the triangle formed by the celestial body and the poles of the equator and ecliptic relates equatorial and ecliptic coordinates. See also heliocentric coordinate system.

References in periodicals archive ?
Because the projection of hip joint included angle on coordinate axis relates to multiple factors, in order to simplify analysis, this article only analyses angle variation of hip joint after 3D integration.
infinity]]-spherical cap in the virtual space, define w to be the coordinate axis that is along the x-axis with the origin displaced at ([+ or -]L/2, 0, 0), respectively.
The most important benefit of such non-parallel reference system is that orientation to the baseline for building site network close to the direction of the site grid axis is in many cases more convenient than using a baseline with direction close to the coordinate axis of the national coordinate system.
By computing the terms of(1) corresponding to each coordinate axis and replacing into the energy equation:
These campaigns have enabled better and better determinations of the position of the "zeroes" in three dimensions of a rotating Earth centred coordinate axis system.

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