Accession No


Brief Description

planispheric astrolabe, English [attributed], 14th century






Earliest Date

Jan. 1, 1340

Latest Date

Dec. 31, 1400

Inscription Date


metal (brass); plastic (at the back of the astrolabe between the plate and the fastening)


Mater diameter 295 mm

Special Collection



Description Notes

Brass planispheric astrolabe: mater with inscribed projection, rete, alidade, rule, pin and horse.

Plate is inscribed for latitude 52 degrees (London (?)). A later month calendar has been added within the womb, with letters formed from hammered points, against the scale of degrees on the rim. The attachment of the suspension ring looks weak. There is slight tarnishing and corrosion. What looks like a dent in the rim is the index of the spider (or rete). On reverse are labelled zodiac and calendar scales, divided to single degrees and marked in fives; shadow square for Umbra Recta and Umbra Versa 0 to 12 to 0, marked in twos. Ecclesiastical feast days are marked against the calendar scale. 1st point of Aries is March 15th. H and d (?) have been crudely and lightly scratched against the rim.

Rete, with quatrefoil and semi-quatrefoil motifs. 41 star pointers, 38 labelled. One, with surviving label only EL, is broken off. Other star names are YED, ALRAMEK [?], CAVDA, CENOK [?], MIRAK [=mirach], ALFERAS [?], HVMER’ EQVI, MVSIO ACQVI, DELPHIN, ALTHAYR [=altair], ALHAWE [=alterf?], THABEN [=thuban], WEGA [=vega], ALOIGEGE[?], BENENAZ [=benetnasch], EDVB [=dubhe?], ALHAOR [?], ALGANEB [=algenib], ALDERA [=alderamin?], SKEIOER [?] (within ecliptic); ALACRAB [?]; ALEHIMEK [?], ALGORAB, ALPARD [=alphard], COR, MARKEB, ALHABOR [?], RIGIL, ALGOMEIZA [=gomeisa], ELGEVZE [=betelgeuse], ALDEBORAM [=aldebaran], MENKAR, AVGETENAR [?], BATVCHAYTHOS [=baten kaitos], DENEBCHAYTOS [=deneb kaitos], CENOR [?], DENEBALGEDI [=deneb algedi] (outside ecliptic). One unlabelled pointer in the form of a bird. Ecliptic is labelled with Latin zodiacal signs, divided to 2 degree units, and marked in sixes.

Alidade is counter-changed, with soldered vanes bearing twin pin-hole sights. Counter-changed rule bears unlabelled division marks. Pin has one brass and two plastic washers.

[NOTE: On 06/12/2013 XRF analysis was conducted on this instrument. Results and analysis are given in the ‘Notes’ field and in the OHF.]


Catherine Eagleton; 'A 14th-century English astrolabe'; Explore Whipple Collections online article; Whipple Museum of the History of Science; University of Cambridge; 2008:


The astrolabe was a key astronomical instrument during the Middle Ages. It is a calculating device that can be used to tell the time, measure the heights of stars and buildings, and for many other calculations and observations. It works because it is a 2-dimensional representation of the 3-dimensional Universe as understood by the medieval astronomer - with the Earth at the centre of the apparent motion of the Sun.

This particular instrument was probably made in the 14th century, and is typical of medieval English astrolabes. It has been engraved so that it will work at the latitude 52 degrees. This is the latitude of London, so it is reasonable to suppose that it was intended for use in or near the capital.

The rete, a cut-out plate with pointers showing the position of stars, rotates over the projection of the celestial sphere. Most of the 41 pointers here are labelled with the names of stars, many of them in Arabic, reflecting the Arab influences on medieval European astronomy.

On the back of the astrolabe are eccentric circles for calculations relating to the calendar. As well as a zodiac calendar, there is also a calendar in which saints' days and feast days are marked, providing a handy reference for a medieval religious person. We know that monks, friars and clerics were among those who owned astrolabes in the Middle Ages. This doesn't necessarily mean that this astrolabe was made for a religious person - these kinds of scales would also be useful for a politician or a merchant, since the medieval calendar was organised around saints' days and religious festivals.

Created by: [Adapted from Catherine Eagleton’s 2008 Explore article] on 19/12/2013


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