A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Ed Popko
Date: 2019 Aug 7, 07:14 -0700
I keep thinking about this eclipse image.
I assume in this eclipse puzzle we dont know our latitude, otherwise we could simply shoot the sun to get local time, compare it with GMT and have our longitude/latitude by traditional time sight method. An eclipse is a more interesting problem than a standard time sight.
This may be totally wrong thinking but in an eclipse, I think one sees totality only when they are visually (eye-ray wise) aligned from my vantage point, not necessairly when they both sun/moon have the exact same GHA/Dec Ground Point. If they were equal, I would be at the ground point of both bodies; the eclipse would be directly over my head. Clearly the eclipse image we are looking at shows we are quite a ways away from their Ground Points. Other observers along the eclipse-band will see their personal-totality as the line between the centers of the sun and moon sweeps across the earth. And yes, there is a totality dwell time just like LAN so the GMT of my personal totality is imprecise.
But the moon's GHA/Dec is not the same as the sun's GHA/Dec. It will be close-to but not exactly equal to the sun's because the totality sweeps across the earth since the moon is moving at a different rate across the sky. The totality I see occurs at a different GMT than others along the eclipse band as it sweeps across the earth.
So, if we know the GMT of our 'personal totality', and the GHA/Dec of both sun and moon at that instance, is there a way to use this slight difference to find our position?