Dictionary:Transit

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1. A precision instrument for measuring horizontal and vertical angles. It consists of a telescope mounted so as to swivel vertically and secured to a revolvable table carrying a vernier for reading horizontal angles. A graduated circle for measuring vertical angles and a compass and level are also included. Also called transit-theodolite. ‘‘Transit’’ and ‘‘theodolite’’ are largely interchangeable, American usage generally favoring the first, European usage the latter. Usually a transit has an open vernier and a built-in compass whereas a theodolite has a micrometer and a detachable compass. An especially precise transit is sometimes called a theodolite. An accuracy of about 10 seconds of arc can be achieved, though 30-second accuracy is more likely. See Figure T-12. 2. The passage of a celestial body across a celestial meridian. 3. The passage of a satellite involved in satellite navigation. ‘‘Transit’’ was the system name of the former Navy Navigation Satellite System.