Celestial Sphere

An imaginary sphere of infinite radius centered on the Earth and poles aligned with the poles of the Earth.

A point on the celestial sphere is really only a direction in space. Parallel lines meet the celestial sphere at the same point.

Antisolar Point

The point on the celestial sphere 180° from the sun.

Apparent Position

The position on the celestial sphere at which a heavenly body would be seen from the centre of the earth at a particular time.

Astrometric Position

The position of a heavenly body (or space vehicle) on the celestial sphere corrected for aberration but not for planetary aberration.

See also: Nadir.

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Subjects: Astronomy