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Paul, you wrote:
"It turns out that Apple's iPhone and iPod Touch make a nifty
artificial horizon.  Both devices have built-in angle/acceleration
sensors, so If one downloads Labyrinth Lite (currently the most
popular game download for the iPod), it has a set-up feature that
displays two right-angle leveling bubbles.  Use a couple of Post-its
to shim it into level and the screen makes a small but effective
sighting surface!  I haven't actually tried to measure the leveling
sensitivity, but my wild guess (based on how hard it isto chase the
bubble) it is something like a 10 - 30 min bubble equivalent."

:-)

A simple app that could be written would measure the angular tilt of the
device and record it when the screen is tapped. One could then aim the
device at the Sun by minimizing its shadow, and then immediately read out
the altitude. As you say, these altitudes are only accurate to 30 minutes of
arc or maybe somewhat better, but you might still be able to extract some
useful navigational information out of it (and this would work even if the
device has no access to network information/cell phone capability). It might
make a very good digital compass...

There are off-the-shelf digital levels available that measure angles to
about +/-10 minutes of arc reliably (at 6' nominal precision). You could
stick a simple sighting tube on top of one and you have a digital "sextant"
in no time. But a device like this is not that useful for manual
observations. It abandons the most important trait of the sextant:
double-reflection. Without double-reflection, we're right back to the days
of the backstaff or the kamal, and shaky hands are the limiting factor in
taking sights. So I guess in the end, I would call a device like this a
"digital kamal" rather than a digital sextant.

 -FER



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