Make your own Astrolabe
An astrolabe is an elaborate instrument which combines a mechanical model of the sky's rotation through the night – similar to a modern planisphere – with an observing instrument which allows the altitudes of objects in the night sky to be measured. Put together, these two components can be used the time of day, by determining the altitude of a star, and also at what time of day the sky's rotation brings it to that height above the horizon.
Historically, the astrolabe was the most sophisticated astronomical instrument in widespread use in the Middle Ages. In fact, it held this position for nearly two thousand years, from the time of Hipparchus (c. 190–120 BCE) until the turn of the seventeenth century, around the time that the telescope was invented in 1609.
Yet today this complex instrument is rarely seen outside of glass cases in museums, and those interested in learning about it may have some difficulty finding a specimen to play with. Ornately carved brass reproductions are available from some telescope dealers, but with substantial price tags attached. These price tags are historically authentic: mediaeval astrolabes were often made from high-cost materials and intricately decorated, becoming expensive items of beauty as well as practical observing instruments. But for the amateur astronomer who is looking for a toy with which to muse over past observing practice, a simpler alternative may be preferable.
On this webpage, you can download a cardboard cut-and-glue kit to make your own model astrolabe, so that you can rediscover medieval observing practice for yourself.
What you need
- A printer (to print your astrolabe kit)
- Three sheets of thin card or paper
- A sheet of transparent plastic, e.g. acetate, which is safe to put through a printer
- A split-pin fastener
- A short piece of ribbon or string
Step 1 – Download our astrolabe kit (a PDF file). The exact layout of a astrolabe depends where on Earth it's designed to be used from, since different stars are visible in the night sky from different places. We can supply a custom kit designed for use where you live. For your present location of Ashburn, we recommend a astrolabe designed for latitude $bestLatStr, which you can download here.
To download a astrolabe for use at a different latitude, use the form below:
Step 2 – Print figures 1, 2 and 3 from the PDF file onto separate sheets of paper, or more preferably onto thin card. Print figure 4 onto a sheet of transparent plastic, such as acetate sheets sold for use with overhead projectors.
Step 3 – Cut out figures 1 and 2, which show the front and back sides of the astrolabe, and glue them back to back. You may wish to sandwich a piece of cardboard between them to make your astrolabe more rigid.
Step 4 – Place figure 4 (the rete), printed on the transparent plastic, over the front of the astrolabe.
Step 5 – Cut out the rule and the alidade in Figure 3. The rule (on the left) should be placed over the top of the rete, on the front side of the astrolabe, while the alidade should be placed on the back of the astrolabe.
Step 6 – Now all of the parts of the astrolabe need to be fixed together with a split-pin fastened. All of the components have small circular holes marked, which you should cut out. This can be done either using a paper drill, if available, or with the point of a compass, turning the point in circles to gradually enlarge a hole to around 2mm across. Once all the holes are made, slide a split-pin fastener through the rule, rete, mother and alidade of the astrolabe in turn, and fold the split pins back to fasten the astrolabe together. Ensure that the central hole is big enough that the alidade, rete and rule can turn freely.
Congratulations, your astrolabe is now ready for use!
Where to find more information
For a full description of how to use a medieval astrolabe, see the paper which I published in the Journal of the British Astronomical Association.
Much more historical information about the astrolabe can be found in John North's 1998 book Cosmos.
Like everything else on this website, these astrolabe kits are © Dominic Ford. However, they are provided for the benefit of amateur astronomers worldwide, and you are welcome to modify and/or redistribute any of the material on this website, under the following conditions: (1) Any item that has an associated copyright text must include that unmodified text in your redistributed version, (2) You must credit me, Dominic Ford, as the original author and copyright holder, (3) You may not derive any profit from your reproduction of material on this website, unless you are a registered charity whose express aim is the advancement of astronomical science, or you have the written permission of the author.
This astrolabe kit was designed using a vector graphics scripting language called PyXPlot. If you have PyXPlot installed on your computer, you can download the scripts used to generate this model as a zip archive.