Danjon astrolabe

astronomy

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June 25, 2026

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The Danjon astrolabe is a specialized astronomical instrument developed by French astronomer André-Louis Danjon. It is a modern version of the astrolabe, designed for precise measurements of star and planet positions. This instrument can also be used to determine an observer's latitude and longitude if star positions are known.12

The Danjon astrolabe, introduced in 1956, features a small aperture (8-10 cm) and utilizes a pool of mercury and a prism. It works by observing a direct image alongside an image reflected off the mercury to gather positional data. This instrument was widely adopted, with over 30 major observatories using it within four years of its introduction. Danjon also used this and other precise instruments to study irregularities in Earth's rotation, noting a correlation between sudden increases in the Earth's rotational period and intense solar activity.21

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André-Louis Danjon
…astrolabe, now known as the Danjon astrolabe. Within four years of its introduction (1956), the Danjon astrolabe was being used in more than 30 major observatories.
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…astrolabe, now known as the Danjon astrolabe. Within four years of its introduction (1956), the Danjon astrolabe was being used in more than 30 major observatories.
Read More