A Treatise on the Astrolabe

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So-called Chaucer Astrolabe dated 1326, similar to the one Chaucer describes, British Museum

A Treatise on the Astrolabe is a medieval instruction manual on the astrolabe by Geoffrey Chaucer. It is notable for being written in prose, in English and for describing a scientific instrument.

Line numbers are taken from Robinson (1983), though as the original is prose they refer to this edition only.


The Treatise is considered the "oldest work in English written upon an elaborate scientific instrument".[1] It is admired for its clarity in explaining difficult concepts—although modern readers lacking an actual astolabe may find the details of the astrolabe difficult to understand. Robinson believes that it indicates that had Chaucer written more freely composed prose it would have been superior to his translations of Boece and Melibee.[2]


The work is written in free flowing contemporary (1391) English, today commonly referred to as middle English. Chaucer explains this departure from the norm thus:

"This treatis, ..., wol I shewe the ... in Englissh, for Latyn ne canst thou yit but small"[3][a]

Chaucer proceeds to labour the point somewhat:

"Grekes ... in Grek; and to Arabiens in Arabik, and to Jewes in Ebrew, and to Latyn folk in Latyn; whiche Latyn folk had hem [conclusions] first out of othere dyverse languages, and writtem hem in her owne tunge, that is to seyn, in Latyn.".[4][b]

He continues to explain that it easier for a child to understand things in his own language than struggle with unfamiliar grammar; commonplace today but radical in the fourteenth century. Finally he appeals to Royalty (his wife was a lady-in-waiting to Edward III's queen and sister to John of Gaunt's wife) in an early version of the phrase "the King's English":

"And preie God save the King, that is lord of this language, ..."[5][c]


Skeat identifies 22 manuscripts of varying quality. The best he labels A, B and C which are MS. Dd. 3.53 (part2) in the Cambridge University Library, MS. E Museo 54 in the Bodleian and MS. Rawlinson, Misc. 1262 also in the Bodleian.[6] A and B were apparently written by the same scribe, but A has been corrected by another hand. Skeat observes that the errors are just those described in "Chaucers Wordes unto Adam, His Owne Scriveyn":

"So ofte a-daye I mot thy werk renewe,
"It to correcte and eek to rubbe and scrape;
"And al is thorough thy negligence and rape."[d]

A has indeed been rubbed and scraped then corrected by another hand. This latter scribe Skeat believes to be a better writer than the first. To this second writer was the insertion of diagrams entrusted.[7] A and B were apparently written in London about the year 1400, that is some 9 years after the original composition.[7] Manuscript C is also early, perhaps 1420 and closely agrees with A.[8]


Chaucer opens with the words "Lyte Lowys my sone"[9][e]. In the past a question arose as to whether the Lowys was Chaucer's son or some other child he was in close contact with. Kittredge suggested that it could be Lewis Clifford a son of a friend and possible a godson of Chaucer's. As evidence he advanced that Lewis Clifford died in October 1391, the year of the composition, which could explain its abandonment.[2] Robinson reports though the finding of a document by Professor Manly "recently" (to 1957) which links one Lewis Chaucer with Geoffrey's eldest child Thomas Chaucer. The likelihood therefore is that the dedication can be taken at face value.[2]

Chaucer had an eye to the wider public as well. In the prologue he says:

Now wol I preie mekely every discret persone that redith or herith this litel tretys..."[10][f]


Chaucer's introduction to the work lays out his planned structure:

  1. A description of the astrolabe
  2. A rudimentary course in using the instrument
  3. Various tables of longitudes, latitudes, declinations, etc.
  4. A "theorike" (theory) of the motion of the celestial bodies, in particular a table showing the "very moving of the moon"
  5. An introduction to the broader field of "astrologie," a word which at the time referred to the entire span of what we now divide into astrology and astronomy.

However he only completed parts 1 and 2, plus a small collection of "Supplementary Propositions".

The astrolabe[edit]

For more details on this topic, see Astrolabe.

The astrolabe was a sophisticated precision instrument. With it one could determine the date, time (when the sky was clear), the position of stars, the passage of the zodiac, latitude on the earth's surface, tides and basic surveying. Care must be taken not to dismiss the astrological aspects; as well as any mystical interpretation astrological terminology was used for what today would be recognized as astronomy. Determining when the sun entered a house (or sign) of the zodiac was a precise determination of the calendar.

Skeat produced a number of sketches to accompany his edition:

The stars listed on the rim of the rete of the drawings in the Treatise are given below with their modern names:[citation needed]

Name on Rete Modern Designation
Alkab Iota Aurigae
Alpheta Alpha Coronae Borealis
Alramih Arcturus
Alkaid Eta Ursae Majoris
K.Alasad Alpha Leonis
Algomisa Procyon
Alhabor Sirius
Alghul Beta Persei
Alnath Beta Tauri
Markab Alpha Pegasi
Alradif Delta Cephei
Alnasir Alpha Andromedae



  1. ^ "This treatise, ..., will I show you ... in English, for Latin you can only as yet [understand] a little"
  2. ^ "Greeks ... in Greek; and to Arabians in Arabic, and to Jews in Hebrew, and to Latin people in Latin. Latin people had them [results] first out of other diverse languages and wrote them in their own tounge, that is to say, in Latin."
  3. ^ preie = pray
  4. ^ "Often, I must redo your day's work,
    "Correct it and even rubout and scrape [the ink off the surface];
    "All due to your negligence and corruption [of the text]."
  5. ^ "Little Lewis, my son"
  6. ^ "Now I would meekly ask every individual person that reads or hears this little treatise..."


  1. ^ R T Gunther (author: Early Science in Oxford) quoted by Robinson 1983, p. 545
  2. ^ a b c Robinson 1983, p. 545.
  3. ^ Robinson 1983, Prologue lines 25–27.
  4. ^ Robinson 1983, Prologue lines 30-36.
  5. ^ Robinson 1983, Prologue lines 56–57.
  6. ^ Skeat 1900, Introduction, sections 2-4.
  7. ^ a b Skeat 1900, Introduction section 2.
  8. ^ Skeat 1900, Introduction section 4.
  9. ^ Robinson 1983, Prologue line 1.
  10. ^ Robinson 1983, Prologue lines 41–42.


  • Laird, Edgar (1997), "Astrolabes and the Construction of Time in the Late Middle Ages", in Poster, Carol; Utz, Richard, Constructions of Time in the Late Middle Ages (Evanston, IL: Northwestern University Press): pp 51–69 
  • North, J D (1988), Chaucer's Universe, Oxford: Clarendon Press 
  • Robinson, F N, ed. (1983) [1st ed 1933], The Complete Works of Geoffrey Chaucer (2nd ed.), Oxford University Press, ISBN 0-19-281157-6  5th impression. Originally published by Houghton Mifflin Co, Boston, Mass.
  • Skeat, Walter W, ed. (1900), The Complete works of Geoffrey Chaucer, Vol III (2nd ed.), Oxford University Press  (note that the title page incorrectly gives a date of "M DCCCC")

External links[edit]