A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Geoffrey Kolbe
Date: 2021 Feb 19, 22:25 -0800
Frank said: "If you sweep a great circle from the Sun to the Moon, you will find that it hits the Moon dead-center on the illuminated limb."
That is more easily said than done. But when I am doing a lunar I usually take the telescope out of the sextant to get a good field of view. Then, sighting the Moon through the horizon mirror, I rack the index arm until the Sun appears. The Sun will only appear, however, if I set the sextant perpendicular to the Moon's Horns. I am, effectively, putting the sextant on the plane of the great circle between the Moon and the Sun.
At that point, of course, I put the telescope back in and make the small adjustment necessary so that the to bodies touch.