A great circle on the celestial sphere passing through the celestial poles and an observer’s zenith. An observer’s celestial meridian is not a fixed reference on the celestial sphere but rather changes with the observer’s location on Earth. Stars transit an observer’s celestial meridian (that is, cross directly overhead in the sky at that location) once every 24 hours. Also called local meridian, meridian.
In the equatorial coordinate system, a great circle on the celestial sphere passing through the celestial poles and the vernal equinox. It represents the zero point for the horizontal coordinate in this system, having a right ascension of 0 hours.
navigation by means of observations made of the apparent position of heavenly bodies. noun navigation by observation of the positions of the stars Also called astronavigation celestial navigation Navigation of a ship or aircraft based on the observed positions of celestial bodies. See more at altazimuth coordinate system.
each of the two points in which the extended axis of the earth cuts the celestial sphere and about which the stars seem to revolve. noun either of the two points at which the earth’s axis, extended to infinity, would intersect the celestial sphere Sometimes shortened to pole celestial pole Either of the two points […]
the imaginary spherical shell formed by the sky, usually represented as an infinite sphere, the center of which is a given observer’s position. noun an imaginary sphere of infinitely large radius enclosing the universe so that all celestial bodies appear to be projected onto its surface celestial sphere An imaginary sphere with Earth at its […]
a transparent celluloid sheet on which a character, scene, etc., is drawn or painted and which constitutes one frame in the filming of an animated cartoon: may be overlapped for change of background or foreground. Historical Examples noun short for celluloid (sense 2b), celluloid (sense 2c) n. “celluloid sheet for an animated cartoon,” from celluloid; […]