Treatise on the Astrolabe

work by Chaucer

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July 14, 2026

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Geoffrey Chaucer, renowned for The Canterbury Tales, also authored A Treatise on the Astrolabe. This work served as a user's guide to the astrolabe, an early scientific instrument used for timekeeping and astronomical observations. Chaucer wrote the treatise in English, rather than the typical Latin, to make it accessible to his young son, Lewis, who had an aptitude for mathematics.12

The planispheric astrolabe, a common type, allowed astronomers to calculate the positions of the Sun and stars relative to the horizon and meridian. It functioned as a rudimentary analog computer, depicting the celestial sphere and key astronomical circles. Astrolabes were widely used in the Middle Ages in Europe and the Islamic world, and later adopted by mariners for celestial navigation before being superseded by sextants.2

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Geoffrey Chaucer
Descendants and legacy of Geoffrey Chaucer
In 1391 Chaucer had written Treatise on the Astrolabe for “little Lewis,” probably his younger son, then 10 years old. Elizabeth “Chaucy,” probably the poet’s daughter, was a nun at Barking in 1381. A second probable daughter, Agnes Chaucer, was a lady-in-waiting at Henry IV’s coronation in 1399. Speculation that…
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In 1391 Chaucer had written Treatise on the Astrolabe for “little Lewis,” probably his younger son, then 10 years old. Elizabeth “Chaucy,” probably the poet’s daughter, was a nun at Barking in 1381. A second probable daughter, Agnes Chaucer, was a lady-in-waiting at Henry IV’s coronation in 1399. Speculation that…
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navigation
The lodestone and the compass card
…by Geoffrey Chaucer in his Treatise on the Astrolabe (1391). It also has been said that the navigators of Amalfi, Italy, first expanded the number of compass points to 32, and they may have been the first to attach the card to the needle.
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…by Geoffrey Chaucer in his Treatise on the Astrolabe (1391). It also has been said that the navigators of Amalfi, Italy, first expanded the number of compass points to 32, and they may have been the first to attach the card to the needle.
Read More