Meridian circle

Meridian circle at the Kuffner observatory, Vienna, Austria, built by Repsold & Sons, Hamburg, 1886. Note the counterweights, the short, green cylindrical objects at the outer top of the mechanism, and the four long, thin, microscopes for reading the circles.

Top view of a circle-reading microscope; from Norton (1867).

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.

单词	Meridian circle
释义	Meridian circle 英语百科 Meridian circle 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.
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