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Re: Loss of accuracy using Sun over Sun with a mercury artificial horizon?
From: Peter Monta
Date: 2016 Jul 18, 23:47 -0700

Geoffrey Kolbe writes:

Using a theodolite to determine azimuth, the sun simply rushes across the field of view towards the cross-hairs in the 30x scope and it is possible to determine the moment when the sun is tangential to the vertical cross-hair to better than a second.

I wonder if it would be worth driving the theodolite or sextant to improve this situation. Many theodolites these days are "robots" with internal motors capable of driving the instrument axes. If the theodolite were told to "follow the sun", aligning the solar edge with the reticle would become a comfortable no-pressure task, improving accuracy.

The impersonal micrometer on a 19th-century transit instrument did the same thing.

But if a theodolite also has an integrated camera for automatic target recognition, then it could be used to simply image the entire solar disk (with solar filter fitted to avoid destroying the camera and EDM!) and derive an azimuth from that, without asking the user to do any alignment task at all. It might be a little less accurate.

For the sextant, motorize the tangent screw with a clutch and shaft encoder or other readout, then dial in the tangency of the two telescope objects at leisure---they will remain motionless.

Cheers,

Peter

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