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This may be a silly question, in which case some pundit will explain why.

Every sextant I have seen, or seen described or pictured, has a similar
form. The observer looks horizontally through the telescope, at the
horizon, through the part-silvered horizon mirror. The celestial body is
viewed, by reflection in two mirrors, brought down to the horizon by moving
the index arm.

And yet, for some applications, it's useful to use the sextant upside-down,
pointing the telescope at a star, and working the index arm to bring the
view of the horizon (as seen in the "index mirror") up to it. That makes it
easier to identify the right star of a constellation, because the observer,
and his telescope, and his left eye also, are looking up directly at it. In
that case, a pair of open sights could be attached to the telescope, for
easy preliminary sighting without magnification. Then, after identifying
the star in the telescope, it could be kept in view while the horizon (and
there's only one horizon, so never any difficulty in identifying THAT) is
brought up to meet it.

The trouble is that no sextant that I know of has been designed to be used
that way, so the handles and knobs are all in completely the wrong place.
That in itself is enough to discourage the use of a sextant "upside-down".

I can see one advantage to the "normal" use of a sextant, in that the
observer always looks in a horizontal direction, which is comfortable for
him. Use in "upside-down" mode requires him to look up into the sky, which
might be an uncomfortable posture, especially if the altitude was great. Is
that the only reason (or the dominant reason) why EVERY sextant is made the
way it is?

Has any maker ever experimented with a design which would make it easier to
use a sextant "upside-down", or better still, either way, perhaps by
providing an additional handle and an extended adjustment knob? That, by
the way, would also ease the measurement of lunars.

I only ask...

George.

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