Next message: Fuller, Michael D: "Re: Knot Question"
Frank,
Here's another way of looking at the problem.
The sextant is designed to measure an arc of a great circle. That circle is
in a plane perpendicular to the axis of the instrument. The axis is a supposed
line drawn lengthwise through the center of the pivot behind the index mirror.
Your eye and two stars form another plane. As long as this second plane is
perpendicular to the axis of the sextant, the sextant can accurately measure the
great circle distance between the stars. If it is not perpendicular to the
axis the angle will measure too great.
This is a serious problem only with large angles. You might experiment by
measuring the distance between two stars 110 or 120 degrees apart. Move them back
and forth across the field of view and see what happens.
Bruce
