transit-1 (a) 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. (b) The apparent passage of a star or other celestial body across a line in the reticle of a telescope, or some line of sight. (c) The apparent passage of a smaller celestial body across the disk of a larger celestial body. When no line is specified, a transit across the meridian is usually intended. The transit of a star across the meridian occurs at the moment of its culmination, and the two terms are sometimes used as having identical meanings; such usage is not correct, even where the instrument is in perfect adjustment. At the poles, a star may have no culmination but it will transit the meridians. The transit of a small celestial body across a larger one is exemplified by the transit of the planet Mercury across the disk of the sun, or of a satellite of Jupiter across the disk of that planet. 2 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. 3 v. The act of making such a reversal. A theodolite having a telescope that can be transited in its supports is a transit, and it is sometimes referred to as transit theodolite. 4 An astronomical instrument with a telescope which can be so adjusted in position that the line of sight may be made to define a vertical circle; astronomical transit, transit instrument. See also culmination.

transit, broken telescope—A precise astronomic transit or theodolite in which the light passing through the objective is reflected through a right angle by a prism placed in the trunnion axis. This hollow axis is continued beyond the supports, and the eyepiece is fitted at one end.

transit, jig—A shop instrument for the precise layout of large equipment (i.e., turbines) and aircraft. Resembles the normal transit, but has no compass box, and provides for special attachments for auto-collimation, auto-reflection, or an optical micrometer.

transit, solar—See solar transit.

transit and stadia survey—See survey, transit and stadia.

transit line—See line, transit.

transit micrometer—See micrometer, transit.

transit rule—See balancing a survey, transit rule.

transit traverse—See traverse, transit.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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