NavList:

Matus Tejiscak, a week ago, you wrote:
"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. "

I think you're suggesting using the central slope. The slope in brightness near the middle of the penumbral shadow shoulr provide a good surrogate for the true width of the penumbra, and that should work even when constrast modifications in the image might make it more difficult to estimate the penumbra width, which I think is possible in this image. That's a great idea, if I'm following your thinking here...

The penumbral curve is similar to a related problem where I have used the central slope before: a simple tidal height curve. Suppose you know that a half-cycle of an ocean tide from low to high lasts 6.25 hours. That's typical for semi-diurnal tides. In the vicinity of middle tide (halfway between high and low), you observe that the tide is rising at, let's say, 50cm per hour. From this we can estimate the total tide height range from low to high. The slope in the middle is higher than the simple rate from high to low over the 6.25 hour period by about 57% (a factor of pi/2). A rate of 50cm/hr at mid-tide should correspond to a tidal range of about 2.0 meters. That's about right, isn't it? (I'm doing the numbers in my head as I type, so I might be missing a factor of two somewhere)...

Meanwhile, more confirmation of the overall scale appeared in some images/video released by Firefly Aerospace within the past week showing the view looking straight down as the Blue Ghost lander was settling down on that crater rim. The images below show my attempt to identify small craters and other features around that larger crater. Given the height above the lunar surface before landing, as tagged in the image, the size of the crater that the spacecraft landed on looks to be consistent with your calculations, about 12 meters diameter.

Frank Reed
Clockwork Mapping / ReedNavigation.com
Conanicut Island, North America

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