NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Matus Tejiscak
Date: 2025 Mar 9, 05:41 -0700
I had some doubts where to put the "end of the penumbra" on the plotted curve. Theoretically the shape should be a certain sigmoid so I eyeballed my original penumbra range as pixels 22 through 50, rather than looking at the straight part of it. I was curious what would happen if I just extended the conspicuously straight portion of the line and saw where it crosses the target luminance of about 0.65. That yields a penumbra range of pixel 22 to about pixel 40, so 33' per 18 pixels, which in turn yields the distance to the shadow of 10m.
At this point, I cannot fairly assess which of the choices is the more accurate one but I find it reassuring that plausible guesses revolve around the same range of answers, rather than diverging from it.
Matus
