Definition

In ASTRONOMY, the apparent passage of a STAR or other CELESTIAL BODY across a defined line of the CELESTIAL SPHERE, as a MERIDIAN, PRIME VERTICAL, or ALMUCANTAR. When no line is specified, a transit across the MERIDIAN is usually intended. See MERIDIAN TRANSIT. The apparent passage of a STAR or other CELESTIAL BODY across a line in the RETICLE of a TELESCOPE, or some LINE OF SIGHT. The apparent passage of a smaller CELESTIAL BODY across the disk of a larger CELES­TIAL BODY. A surveying instrument composed of a HORIZONTAL CIRCLE graduated in circular measure and an ALIDADE with a TELESCOPE which can be reversed in its supports without being lifted therefrom. Also, the act of making such a reversal. A THEODOLITE having a TELESCO­PE that can be transited in its supports is a transit, and is sometimes termed a transit theodolite. All modern THEODOLITES are transits. An astronomical instrument having a TELESCOPE which can be so adjusted in position that the LINE OF SIGHT may be made to define a VERTICAL CIRCLE. A transit used in astronomical work is usually termed either an astro­nomic­(al) transit or a transit instrument. In NAVIGATION, the position of two distant, fixed objects when they are in line to an observer; the line passing through them and the observer being a LINE OF POSITION. See also RANGE.