alidade

instrument

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Last updated

June 18, 2026

Quick Summary

An alidade is a rule with sights used to determine direction. It is a component of an astrolabe, an early scientific instrument used for timekeeping and astronomical observations. The planispheric astrolabe, a common type, allowed users to calculate the positions of the sun and stars relative to the horizon and meridian. The alidade on an astrolabe could also be used for surveying, such as measuring the height of a mountain. The word "alidade" originates from the Arabic term for "the revolving radius of a circle" and has been in use since the 15th century.12

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armillary sphere
…with diametric sight rules, or alidades, and it is likely that those made and used in the 12th century by Moors in Spain were the prototypes of all later European armillary spheres.
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…with diametric sight rules, or alidades, and it is likely that those made and used in the 12th century by Moors in Spain were the prototypes of all later European armillary spheres.
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astrolabe
…and a straight rule (the alidade), used for sighting objects in the sky. The alidade made it possible to use the astrolabe for surveying applications—e.g., determining the height of a mountain. Most astrolabes also had one or more plates (called climates) that were engraved with coordinate lines for different latitudes…
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…and a straight rule (the alidade), used for sighting objects in the sky. The alidade made it possible to use the astrolabe for surveying applications—e.g., determining the height of a mountain. Most astrolabes also had one or more plates (called climates) that were engraved with coordinate lines for different latitudes…
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surveying
History
…sights for accurate aim (the alidade) to the objects to be mapped—along which lines are drawn. It was the first device capable of recording or establishing angles. Later adaptations of the plane table had magnetic compasses attached.
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…sights for accurate aim (the alidade) to the objects to be mapped—along which lines are drawn. It was the first device capable of recording or establishing angles. Later adaptations of the plane table had magnetic compasses attached.
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