Tuesday, October 7, 2008
The Astrolabe and Time Zones
When we were working with the astrolabes, I was struck by how it can be used to measure time. Specifically, I was surprised to hear that there was a time factor that we must use to match up the time on the astrolabe and the time on our clock. It made me rather sad that, despite all the progress we have made in the sciences, there are still great errors in our time. In South Bend, we are serious victims of this problem. Because we are on the western end of the Eastern Time Zone, we have very late sunrises and very late sunsets. South Bend is never on its true time, which falls somewhere in between the Eastern and Central Time Zones. It is upsetting to know that we almost never will be living on true solar time. Is there anyway to fix this problem? Or is the inconveniences that would arise from putting people a time that is more precise not be worth living in this more exact time?
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Until the nineteenth-century, each town and city in the world kept to its own local mean solar time -- that's the same time on the astrolabe, differing from the sun only by the 15 minutes back and forth of the Equation of Time (due to the eccentricity of the sun's motion). So, until quite recently, everyone's clock or wristwatch agreed more or less with sundials and (had they still used them in the 19th century!) astrolabes.
What made this untenable was the rise of rapid transit. Towns that used to be a day's journey from each other were now only an hour or two apart by train. Aside from the inconvenience of having to change your watch frequently on a long journey, railway timetables were almost impossibly complicated. Standardized timezones were first adopted on the rail network (and called "railway time"); when their convenience became obvious, they were adopted by international convention.
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