Equatorial coordinate system

The equatorial coordinate system is a <a href="/facts/Celestial_coordinate_system/23HhqvHj">celestial coordinate system</a> widely used to specify the positions of <a href="/facts/Astronomical_object/BCHLa0Q2">celestial objects</a>. It may be implemented in <a href="/facts/Spherical_coordinate_system/5cVnNof3">spherical</a> or <a href="/facts/Cartesian_coordinate_system/lkTqvMmB">rectangular</a> coordinates, both defined by an <a href="/facts/Origin_(mathematics)/Lm26tRCB">origin</a> at the centre of <a href="/facts/Earth/HLLmDfj0">Earth</a>, a <a href="/facts/Fundamental_plane_(spherical_coordinates)/n5cWNMq2">fundamental plane</a> consisting of the <a href="/facts/Projective_geometry/rHKSaEbx">projection</a> of Earth's <a href="/facts/Equator/CjaxbVaN">equator</a> onto the <a href="/facts/Celestial_sphere/TYAtXgor">celestial sphere</a> (forming the <a href="/facts/Celestial_equator/P9Lyq2DE">celestial equator</a>), a primary direction towards the <a href="/facts/March_equinox/27hlaADj">March</a> <a href="/facts/Equinox_(celestial_coordinates)/5wkqN4MJ">equinox</a>, and a <a href="/facts/Right-hand_rule/LJe0Qqh4">right-handed</a> convention.
The origin at the centre of Earth means the coordinates are <a href="/facts/Geocentric_model/yIc6na3w">geocentric</a>, that is, as seen from the centre of Earth as if it were <a href="/facts/Transparency_and_translucency/PRryNNW6">transparent</a>. The fundamental plane and the primary direction mean that the coordinate system, while aligned with Earth's <a href="/facts/Equator/CjaxbVaN">equator</a> and <a href="/facts/Geographic_pole/dTShPqll">pole</a>, does not rotate with the Earth, but remains relatively fixed against the background <a href="/facts/Fixed_stars/grlDbIPX">stars</a>. A right-handed convention means that coordinates increase northward from and eastward around the fundamental plane.

Equatorial coordinate system open-in-new

Equatorial coordinate system