The meridian circle is an instrument for timing of the passage of stars across the local meridian, an event known as a transit, 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 zenith, the south point of the horizon, and the nadir. Meridian telescopes rely on the rotation of the Earth 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.
Other articles related to "meridian circle, circle, meridian":
... The Tokyo Photoelectric Meridian Circle is a fully automated photoelectric meridian circle at the Mitaka campus of the National Astronomical Observatory of ...
... Groombridge Transit Circle (1806) Carlsberg Meridian Telescope (Carlsberg Automatic Meridian Circle) (1984) Tokyo Photoelectric Meridian Circle (1985) ...
Famous quotes containing the words circle and/or meridian:
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—Honoré De Balzac (17991850)
“I knew that my vocation was found. I had received the call, and having done so, I was sure my work would be assigned me. Of some things we feel quite certain. Inside there is a click, a kind of bell that strikes, when the hands of our destiny meet at the meridian hour.”
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