the arc of a vertical circle between the horizon and a point or body on the Celestial Sphere.

geographical position in (assumed) Latitude and (assumed) Longitude chosen to facilitate sight reduction.

the horizontal direction of a celestial body or point from a terrestrial point; the arc of the horizon, or the angle at the Zenith between the north part of the celestial meridian or principle vertica [..]

the arc of the horizon, or angle at the Zenith, between the north part or the south part of the celestial meridian, according to the elevated pole, and a vertical circle through the body or point, mea [..]

the Barycentric Celestial Reference System, is a barycentric system of space-time coordinates for the solar system within the framework of General Relativity. The metric tensor to be used in the syste [..]

the primary great circle of the Celestial Sphere formed by the intersection of the Celestial Sphere and the extended plane of the equator. Also called equinoctial

the circle of the Celestial Sphere formed by the intersection of the Celestial Sphere and a plane though the center of the Earth and perpendicular to Zenith-Nadir line.

a Great Circle on the Celestial Sphere through the Celestial Poles and the Zenith. The Celestial Meridian usually refers to the upper branch, that half from pole to pole which passes through the Zenit [..]

the north and south celestial poles are the two imaginary points in the sky where the Earth's axis of rotation, indefinitely extended, intersects the imaginary rotating sphere of stars called t [..]

angular distance north or south of the celestial equator; the arc of an hour circle between the celestial equator and a point on the Celestial Sphere, measured northward or southward from the celestia [..]