Friday, August 28, 2020

Making History | Building a 2000 Year Old Computer

One of the story lines in the novel The Map of Salt and Stars follows an ancient mapping expedition. The only two surveying tools noted in the text are a notebook and an astrolabe. Naturaly I wondered what's the deal with the astrolabe, and could it realistically power this type of endeavor?

I had some vague notion of what an astrolabe was. In my mind's eye it was a sort of primitive sextant. I was mostly, though not completely, wrong. Here's an excellent TED talk on the subject.

In short, the astrolabe is an ancient mechanical computer. Like the slide rule, it consists of various scales that when aligned solve otherwise complex problems. While the slide rule lets you solve math problems, the astrolabe lets you tackle geospatial ones. What direction is North? What time is it? When is sunset? What stars will appear in the sky tonight? What's my latitude? These are just some of the questions the astrolabe can answer; it has a reputation for being quite the information multi-tool.

This explanation suggests that yes, in ancient times an astrolabe may very well have been the primary tool used by map makers and explorers. Consider that it predates the simple magnetic compass by 1,400 years.

Reading about the remarkable prowess of the astrolabe, I naturally decided I had to have one. I figured Amazon would have a cheap knock-off that I could purchase. Alas, that was a dead end. The products that show up when I searched were both pricey and decorative and wouldn't be useful in a field context. Some additional digging, however, turned up another option: I could make my own, for free no less!

I found two projects that allow you to build an impressively detailed and authentic astrolabe:

I found in-the-sky's version first and the assembly process is straightforward. You download the appropriate PDF for your latitude, print it out, cut the pieces out and pin them together to form a rotating disk. The only gotcha is that you need to print one of the pages on a clear sheet of plastic, which you may not having lying around. See below for the supplies I bought to build my own.

The AstrolabeProject is more sophisticated, it requires that you run a Java based program to generate the relevant PostScript files. The reward for putting up with this requirement, however, is that you can customize the finished device in novel ways. I built the in-the-sky version because I found it first, but I can already imagine building v2 using the AstrolabeProject's generator. Another feature of the AstrolabeProject: it has two lengthy documents that describe how to use the finished device, including a 47 page class handout and a 44 page manual.

I purchased a few items to make my in-the-sky version of the astrolabe, including:

  • C-line transparency film - this transparency material worked well with our Canon Laser printer.
  • 1/2" brass paper fasteners - these were ideal for holding the stack of papers that make up the astrolabe.
  • Japanese Screw Punch - this makes punching the required holes a breeze and was a worthwhile investment.
  • OLFA Rotary Circle Cutter - this simplified cutting out the circular parts of the astrolabe. In hindsight I could have lived without it. Like the paper punch, I figured I was investing in a tool that would be useful for future projects.

With the tools in hand, I was able to print and cut out each piece of the astrolabe. I opted to laminate the various paper components to add some heft to the finished product. I used this BIC lighter hack to bend the sights up on the ruler. That worked OK, but I can already envision a better solution for v2.

If paper isn't your thing, you can check out these instructions for a laser cut plastic version, or go crazy and build one by hand from brass (wow!).

I'm now able to hold in my hand the same tool that helped power explorers, astronomers, astrologers and priests over a thousand years ago. This is humbling. I can't wait to get out in the field put the device to use. Move over map, compass, watch and GPS--there's a new player in town.

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