Today my students got their first chance to work with a celestial globe. A celestial globe is basically the embodiment of the Celestial Sphere theory, along with a theory of the Sun's motion that has the Sun moving along the ecliptic at a uniform rate over the course of a year. Given a particular date you can set the position of the Sun on the globe so that it is in the right place among the stars (it has the correct right ascension and declination). You can tilt the axis of the globe to match the latitude of an observer on Earth. Then you can rotate the globe around its axis to orient it for a particular time of day. In this way you can determine the position of the Sun and brighter stars for any observer on Earth on any day of the year at any time of day. It's pretty incredible that such a simple device can tell you so much - but that is exactly the power of a good theory.
My students mostly use the globe to gain more familiarity with the Celestial Sphere theory and the motions of the Sun (what used to be called "spherics"). But my interest in the globe is in the fact that it is a device that embodies theoretical knowledge. I heard a talk a few years ago about embodied knowledge and I was intrigued. There are certainly many astronomical devices that seem to embody theoretical knowledge. The Celestial Globe, or its ancient cousin the armillary sphere, fit the bill. So do sundials, orreries, astrolabes, and the famous Antikythera mechanism.
My response to this idea of embodied knowledge is to wonder to what extent the device itself really embodies knowledge, or to what extent it just serves as an aid to recall knowledge already possessed by the user (and even more so by the maker). I think in most cases the answer lies somewhere between. Without a celestial globe or something like it, I certainly couldn't tell you at what time Aldebaran will rise on May 4 as seen from Rome, Georgia. But with the device I can tell you quite quickly. So there is some knowledge embedded in the device itself that is not already in my mind. At the same time, if I gave a celestial globe to the "man on the street" and said tell me when Aldebaran rises, etc, I doubt he would have much success. It is not enough to the device to embody the knowledge - the user must also understand HOW the device embodies the knowledge, and thus how to extract useful information from the device.
With the celestial globe some of this information is pretty obvious. There are stars and constellations etched onto the plastic surface of the globe, and that embodies knowledge about the arrangement of stars in our sky in a way that almost anyone could interpret without any training. But the other parts of the globe are harder to use. Could an untrained person figure out how to use the thing without guidance? What if the globe was improperly assembled, or if it was broken? Could the untrained user identify the problem? If not, then clearly there are critical parts of the knowledge that is supposedly embodies in the globe which really lie in the mind of the user.
(As a side note: I ordered some replica armillary spheres to show my class. They were ALL improperly assembled. I notified the company, and they seemed unaware of the problem which meant that everyone who had bought one of their armillary spheres in the past didn't really know how to use one. It was just a decoration. Did the armillary sphere embody any astronomical knowledge for these folks? Probably not.)
So I'm still intrigues by the question, but I'm convinced that it presents a false dichotomy. Devices can surely embody knowledge in some way, as shown by the celestial globe. But any device can only embody knowledge in a meaningful way if there are users who know how to extract useful knowledge from the device. Makes me wonder about all the computer simulations I have created. They could be said to embody theoretical knowledge. But if I burn the programs onto a CD and then wait 20 years and find that no computer can run the programs any more (or read the CD!) then can they still be said to embody knowledge? Not in any way that I find worth thinking about.
Speaking of computer simulations, if you want to check out a virtual version of the Celestial Sphere model (with the drifting Sun), see my EJS Celestial Globe Model.
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