The British Museum in Thirteen Objects – The Chaucer Astrolabe

The Chaucer Astrolabe

The Chaucer Astrolabe, British Museum

The astrolabe was a multi-purpose scientific instrument in the Middle Ages. When the illegitimate child of Abelard and Héloise was born in the early twelfth century, he was named Astrolabe in its honour.

An astrolabe, according to James Robinson in Masterpieces of Medieval Art, is a two-dimensional map of the three-dimensional celestial sphere. In much the same way that an Ordnance Survey map can help you find your way through a wood, up hills and over streams you’ve never seen before, so an astrolabe can you to find your way through the heavens. It was, as you can see, a sophisticated instrument.


The Chaucer astrolabe is dated 1326, 16 years before Chaucer was born, and is the earliest dated European astrolabe. Although it didn’t belong to Chaucer, the poet wrote a treatise on the astrolabe, the first in English, and described an instrument very like this. Dedicated to his son Lewis, it was written by 1391. There are more than thirty surviving manuscript copies of the treatise.

Most texts about the construction and use of astrolabes were written in Latin. They were used to tell the time in the many different time systems that existed in fourteenth-century England. It could be used to work out angles and the height of objects. It could also be used while casting horoscopes.

Saints’ days in English and the latitude for Oxford are written on the back, indicating that it was principally for use in England. There are also inscriptions relating to Jerusalem, Babylon, Montpellier and Paris.

It’s just over 5 inches in diameter and less than half an inch thick. The star pointers are shaped like birds.

On the left in my photograph is Richard II’s quadrant. The raised piece that you can see is his emblem: the white hart. It’s a timepiece, enabling its user to tell the time from the angle of the sun. It’s dated 1399, the year of the king’s death.


Masterpieces of Medieval Art


Filed under Fourteenth Century, Medieval Science

16 responses to “The British Museum in Thirteen Objects – The Chaucer Astrolabe

  1. I’ve read about them but never known what they looked like. So I’ve taken a step forward, but I still have no idea how they worked. That, I guess, would fill a Chaucer-sized treatise–and these days it’s not something a person needs to know.

    Liked by 2 people

  2. Fascinating instruments and so sophisitcated. You’ve reminded me that I’ve been meaning to visit the Museum of the History of Science’s collection of astrolabes in Oxford.

    Liked by 2 people

  3. I was familiar with the word but never realised what it was…also I’d nearly have a baby just to call it Astrolabe…..nearly! 😀

    Liked by 3 people

  4. That’s a wowzer bit of kit! Think this is my fave so far in your series.

    Liked by 3 people

  5. I have read about astrolabes and seen a few, but have no idea how to use one. It is on my list of things to do. This one is beautiful.

    Liked by 1 person

  6. I too have heard/read about astrolabes, but had no real idea what they did and am certainly not bright enough to work out how to use one. Yet another reminder, if one was needed, that our ancestors were much more cleverer than we sometimes think they were.

    Liked by 2 people

  7. Yes, Abelard & Heloise were odd. And her uncle & his thugs were pretty nasty dudes. At least they had one child before Abelard’s “big change”!

    The astrolabe was crucial to open water navigation. It was a fearful thing to venture out of sight of land, and chronometers were hundreds of years away. Navigating by the stars must have been crucial. I imagine the astrolabe would help keep the ship’s position as correct as possible. Must have been frightening. I suppose the navigation instruments were carefully protected on ship.

    Imagine accidentally dropping it overboard!

    Such a lovely object. Expensive things were so highly embellished in those days. Suppose if one’s going to shell out a year’s salary for an object, it should be a delight to the eye as well as a critically needed instrument.

    Thank you, Ms. Munday!

    Liked by 1 person

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