Sundials and improvised compasses

I joined iPhone Nation a month or so ago. The iPod touch was my gateway drug. It seemed harmless enough at the time, but things got out of control. Now I’m one of those people. One of those iPhone people. You know the kind. Even I think we’re insufferable.

Anyway, I’ve been having fun with the applications available at the App Store, and one that caught my eye was Masayuki Akamatsu’s Compass. Here’s a little video on how it works.

In a nutshell, here’s the theory. If you know where you are, and you know which way is north, and you know what day of the year it is, you can build a sundial that keeps very accurate time. (If you don’t know what day of the year it is, you can build a sundial that’s reasonably accurate, but that’s another matter.) Stated another way, if you know what day it is, and you know where you are, and you know what time it is, then you can build a sundial that will tell you which way north is. It turns out an iPhone has all the information it needs to build just such a north-pointing sundial. Which is to say: a compass. No magnet required.

I had a similar thought four years ago when I was noodling around with some sundial code in MATLAB. I even wrote a contribution for the MATLAB Central File Exchange called Building Sundials. That contribution came with some explanatory text that closed with this statement.

Suppose you were lost in the woods, equipped with only a computer, a printer, and a copy of MATLAB. How would you orient yourself?

I meant it as a joke, but that’s essentially where the iPhone has gotten us.

Okay, I admit that a real compass is cheaper than an iPhone. And it works at night. Without batteries. And when it’s cloudy. But still… Hey, did I show you my beautiful new iPhone?

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