Astrolabe

an astronomical instrument for taking the altitude of the sun or stars and for the solution of other problems in astronomy and navigation: used by Greek astronomers from about 200 b.c. and by Arab astronomers from the Middle Ages until superseded by the sextant.
Historical Examples

See Chaucer’s own treatise on The astrolabe, which he describes.
Chaucer’s Works, Volume 5 (of 7) — Notes to the Canterbury Tales Geoffrey Chaucer

The rest of the voyage of the astrolabe was in well-known waters.
Celebrated Travels and Travellers Jules Verne

In 1114, the right word is site; cf. the Treatise on the astrolabe (see Note).
Chaucer’s Works, Volume 3 (of 7) Geoffrey Chaucer

This Chaucer says plainly, in his Treatise on the astrolabe, pt.
Chaucer’s Works, Volume 1 (of 7) — Romaunt of the Rose; Minor Poems Geoffrey Chaucer

Chaucer uses the term ‘root’ again in B. 314; and in his astrolabe, ii.
Chaucer’s Works, Volume 5 (of 7) — Notes to the Canterbury Tales Geoffrey Chaucer

Little Lewis had asked him if he might learn something about an astrolabe.
Chaucer’s Works, Volume 3 (of 7) Geoffrey Chaucer

One of the Tables or discs, used by being dropped within the depression on the front of the astrolabe; i. 17.
Chaucer’s Works, Volume 3 (of 7) Geoffrey Chaucer

This, however, was a ‘sufficient’ astrolabe for the purpose.
Chaucer’s Works, Volume 3 (of 7) Geoffrey Chaucer

The astrolabe had anchored in the same depth, and upon a similar bottom.
Celebrated Travels and Travellers Jules Verne

About the early printed editions of the astrolabe, I have not much to say.
Chaucer’s Works, Volume 3 (of 7) Geoffrey Chaucer

noun
an instrument used by early astronomers to measure the altitude of stars and planets and also as a navigational aid. It consists of a graduated circular disc with a movable sighting device Compare sextant
n.

mid-14c., from Old French astrelabe, from Medieval Latin astrolabium, from Greek astrolabos (organon) “star taking (instrument),” from astron “star” (see astro-) + lambanien “to take” (see analemma).
astrolabe
(ās’trə-lāb’)
An ancient instrument used widely in medieval times by navigators and astronomers to determine latitude, longitude, and time of day. The device employed a disk with 360 degrees marked on its circumference. Users took readings from an indicator that pivoted around the center of the suspended device like the hand of a clock. The astrolabe was replaced by the sextant in the 18th century.