Astronomical instrument for timing of the passage of stars
Groombridge transit circle of 1806
The meridian circle is an instrument for timing of the passage of stars across the local meridian, an event known as a culmination, while at the same time measuring their angular distance from the nadir. These are special purpose telescopes mounted so as to allow pointing only in the meridian, the great circle through the north point of the horizon, the north celestial pole, the zenith, the south point of the horizon, the south celestial pole, and the nadir. Meridian telescopes rely on the rotation of the sky to bring objects into their field of view and are mounted on a fixed, horizontal, east–west axis.
The similar transit instrument, transit circle, or transit telescope is likewise mounted on a horizontal axis, but the axis need not be fixed in the east–west direction. For instance, a surveyor's theodolite can function as a transit instrument if its telescope is capable of a full revolution about the horizontal axis. Meridian circles are often called by these names, although they are less specific.
For many years, transit timings were the most accurate method of measuring the positions of heavenly bodies, and meridian instruments were relied upon to perform this painstaking work. Before spectroscopy, photography, and the perfection of reflecting telescopes, the measuring of positions (and the deriving of orbits and astronomical constants) was the major work of observatories.[1][2][3]
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Chauvenet, William (1868). A Manual of Spherical and Practical Astronomy, II. Trubner & Co., London. pp. 131, 282.
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Newcomb, Simon (1906). A Compendium of Spherical Astronomy. MacMillan Co., New York. p. 317ff, 331ff.
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Norton, William A. (1867). A Treatise on Astronomy, Spherical and Physical. John Wiley & Son, New York. p. 24ff.
The meridiancircle is an instrument for timing of the passage of stars across the local meridian, an event known as a culmination, while at the same...
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10th meridian east forms a great circle with the 170th meridian west. Starting at the North Pole and heading south to the South Pole, the 10th meridian east...
the idealized earth is a great circle and any meridian and its opposite meridian form a great circle. Another great circle is the one that divides the land...
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refer to Meridian (astronomy), imaginary circle in a plane perpendicular to the planes of the celestial equator and horizon Central meridian (planets)...
targets Kamal – Celestial navigation device that determines latitude Meridiancircle – Astronomical instrument for timing of the passage of stars Microchannel...
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meridian west forms a great circle with the 90th meridian east, located midway between the Prime meridian and the 180th meridian; thus, the center of the...
groups: meridian, zenith, and universal instruments. For observation of star transits in the exact direction of South or North: Meridiancircles, Mural...
100th meridian east forms a great circle with the 80th meridian west. Starting at the North Pole and heading south to the South Pole, the 100th meridian east...
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celestial meridian (north-south meridian, passing through the zenith) and secondary meridians (circles intersecting the north-south meridian at the zenith)...
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the epoch (e.g. J2000) stated. A meridian on the celestial sphere matches an hour circle at any time. The hour circle is a subtype whereby it is expressed...
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