Palermo altazimuth circle. Historical artwork of Ramsden's altazimuth circle, finished in 1789. The altazimuth circle was a device used to mount an instrument, in this case a telescope, in order that it may move freely along the altitude (vertical) and azimuth (horizontal) axes. Jesse Ramsden, one of the leading instrument makers in the late 18th century, made this circle for the Sicilian astronomer Giuseppe Piazzi at Palermo Observatory, Sicily, Italy. The 5 foot vertical circle was used for constructing his catalogue of stars. Illustration from Pearson's A Treatise on Practical Astronomy (1824).
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