A TREATISE ON THE ASTROLABE

“Lyte Lowys my sone, I aperceyve wel by certeyne evydences thyn abilite to lerne sciences touching nombres and proporciouns; and as wel considre I thy besy praier in special to lerne the tretys of the Astrelabie. Than for as mochel as a philosofre saith, "he wrappith him in his frend, that condescendith to the rightfulle praiers of his frend," therfore have I latitude of Oxenforde; upon which, by mediacioun of this litel tretys, I purpose to teche the a certein nombre of conclusions aperteynyng to the same instrument.”

“Little Lewis, my son, I have prepared a lesson on the astrolabe for you, because I see that you are interested in science. The reasons I have prepared my own treatise in English on the subject are as follows:”

1.No one in our region of England thoroughly understands the astrolabe; 2.I have found mistakes in other manuscripts about the astrolabe; 3.Your Latin is not quite good enough to be reading complex material in that language, and lastly, 4.You are only ten years old, and a simpler treatise written in plain English will help you understand the astrolabe better.

“My son Lewis, as a philisopher once said, “ he wrappeth him in his frend, that condescendeth to the rightful preyers of his frend, ” or in other words, “ a good friend helps out his friend ” which is what I am trying to do by giving you this treatise.”

“Don’t be envious of my knowledge of science; all that I have written here is not my own work, but compiled from other manuscripts. But considere wel, that I ne usurpe nat to have founde this werk of my labour of olde Astologiens, and have hit translated in myn English only for thy doctrine; and with this swerd shal I sleen envye. The treatise has 5 parts: 1. A general description of the astrolabe 2. How to use it 3. Charts concerning latitude and longitude 4. Charts concerning the movements of celestial bodies 5. A general introduction into the theory of astrology\

PART I Here begins the description of your astrolabe: 1.The astrolabe has a hole in it, with which to put your thumb through, for measuring height, or, as I will from now on call it, “altitude”. 2.The ring can also go through a chain, from which the astrolabe hangs down from. 3.The astrolabe consists of plates piled on top of each other. 4.A line crosses the astrolabe: the upper part is called the south line or meridionel, and the lower part is called the north line or the line of midnight.

5. There is also a line running down, creating a cross like this: 6. The left side is west, and the right side is east. 7. The astrolabe is divided into 90 degrees. 8. The astrolabe is divided into the 12 zodiac signs. 9. The astrolabe is also divided into 365 days.

10. Next the cercle of the daies folewith the cercle of the names of the monthes, that is to say, Januarius, Februarius, Marcius, Aprilis, Maius, Junius, Julius, Augustus, September, October, November, December. The names of these monthes were clepid thus, somme for her propirtees and somme by statutes of lordes Arabiens, somme by othre lordes of Rome. Eke of these monthes, as liked to Julius Cesar and to Cesar Augustus, somme were compouned of diverse nombres of daies, as Julie and August. Than hath Januarie 31 daies, Februarie 28, March 31, Aprill 30, May 31, Junius 30, Julius 31, Augustus 31, September 30, October 31, November 30, December 31. Natheles, all though that Julius Cesar toke 2 daies out of Feverer and putte hem in his month of Juyll, and Augustus Cesar clepid the month of August after his name and ordeined it of 31 daies, yit truste wel that the sonne dwellith therfore nevere the more ne lasse in oon signe than in another.

The astrolabe is also marked with months of the year. These are mostly named after Lords of Rome. Julius Caesar, for example, stole 2 days from February, which has 28 days, to put into his month of July. Augustus Caesar has 31 days in his month of August, too. Julius Augustus

12. Next to the A B C lines, there is a scale made up of two squares that is divided into 12 points. The top part is called the Umbra Versa and the bottom part is the Umbra Recta (or Extensa). 13.The alidade (see photo) can be used to determine the sun’s position during the day or the stars’ positions at night. 14. A pin holds the rete and plates to the mater. It acts like the North Pole of the Astrolabe.

15. The womb side of the Astrolabe into four quarters by a cross, just like the other side. 16. The womb side is divided exactly the same way as the other side (see number 7). Chaucer makes it clear that he has said this twice “Now have I told the twyes” 17. Under the rete, the plate is engraved with three circles: Cancer, Aries/Libra, and Capricorn. These three circles or events are important because: Cancer is the summer solstice; Aries/Libra are the equinoxes (where the division between day and night are the same); and Capricorn which is the winter solstice.

18. There are concentric circles engraved on the astrolabe called almuncantars (on diagram Altitude arcs). The zenith is the center of the smallest circle and should be the point directly above your head.

19. Azimuths make right angles with the zeniths. They can be used to find the zenith of the sun or any other star. 20. Twelve divisions under the azimuths indicate planetary hours. 21. The zodiac plays an important role in using the astrolabe. Zodia is a Greek word meaning “beasts” in Latin. Either the sun takes on the characteristics of the beasts when it enters the signs, or the stars are arranged like the beasts, or the planets take on the beastly characteristics when they move through the signs. There can be other effects felt as the planets move through the signs (for example, if a hot planet moves through a hot sign or a cold planet moves through cold sign). Each of the twelve signs also governs parts of the body (Aries=head, Taurus=throat, Gemini= arms and armpits, etc). 19. Azimuths make right angles with the zeniths. They can be used to find the zenith of the sun or any other star. 20. Twelve divisions under the azimuths indicate planetary hours. 21. The zodiac plays an important role in using the astrolabe. Zodia is a Greek word meaning “beasts” in Latin. Either the sun takes on the characteristics of the beasts when it enters the signs, or the stars are arranged like the beasts, or the planets take on the beastly characteristics when they move through the signs. There can be other effects felt as the planets move through the signs (for example, if a hot planet moves through a hot sign or a cold planet moves through cold sign). Each of the twelve signs also governs parts of the body (Aries=head, Taurus=throat, Gemini= arms and armpits, etc).

Form and Dates The Treatise is written in verse form. It contains an introduction and two parts in numbered sections. It is incomplete in that it was intended to contain 5 parts in total. The Treatise on the Astrolabe is dated to around This makes it one of Chaucer’s latest works.

Sources & Manuscripts Aside from The Canterbury Tales, The Treatise on the Astrolabe has the most surviving manuscripts of Chaucer’s work, amounting to 34. The Treatise on the Astrolabe is incomplete. Some versions appear to have been altered slightly by scribes, perhaps because of a desire to make it more scientific and organized. Although the original manuscript has not been ascertained, the oldest versions are believed to have been the versions that contain many diagrams

The Treatise on the Astrolabe is similar to The Man of Law’s Tale, because both emphasize structure, seasons, weather, global location of things, longitude & latitude, and the concept of time. * The Treatise is very socially and culturally relevant because it was a scientific document written specifically for the instruction of those not familiar with academia and was the first known technical manual in the English language.

Chaucer’s treatise was adapted from a treatise written by Arabian astronomer Messahala, who wrote De Compositione et Utilitate Astrolabii in the 8 th century.

National Library of Wales “And for the more declaracioun, lo here the figure:”