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transit telescopeAny telescope that can swing in only one direction, up and down the north-south line in the sky, i.e. the observer's meridian. In optical astronomy a transit circle can be used to determine the positions of celestial bodies. In radio astronomy a transit telescope can be used to build up two-dimensional maps of radio sources: the Earth's daily rotation causes a radio source to move through the beam of the stationary telescope's antenna, providing information in the east-west direction, the direction in which the telescope points being altered slightly each day.
transit telescope[′trans·ət ′tel·ə‚skōp]
A telescopic instrument adapted to the observation of the passage, or transit, of an astronomical object across the meridian of an observer; consists of a telescope mounted on a single fixed horizontal axis of rotation which has a central hollow cube (sometimes a sphere) and two conical semiaxes ending in cylindrical pivots; the objective and eyepiece halves of the instrument are also fastened to the cube of the instrument, perpendicular to the horizontal axis. Also known as transit instrument.