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> Sure. Bauer writes:
> "Swinging an arc is also called rocking the sextant and simply means
> rotating the instrument from side to side around the line of sight to the
> horizon."
>
> And that's not right, but it's a very common error. When this is done
> correctly, the axis of rotation is about the line of sight to the object in
> the sky. If the object is nearly straight up, that means you have to rotate
the
> instrument around a nearly vertical axis.

Thank you Frank,

It seems to me that once seen it is simple, but putting the technique into
words is challenging.  Especially if the motion being described is in error
to begin with.   Somehow I had envisioned a situation where top dead
center of the sextant was affixed to a conceptual ball joint, and the
sextant was swung left to right like a pendulum.

If I understand you in the case of a body near zenith the sextant would be
swung left to right as though it were fixed to ball joints near top dead
center and and bottom center.

I am assuming the axis of rotation (along the line of sight to the body)
would pass through the index mirror.  Is that correct?

Bill

   

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