Here the semi-dameter of the imaged umbra was measured using Image Analyst software with each of the 39 images from Souza and (right) 24 images from Filby, all calibrated with the limb size equal to the semi diameter of the Moon. The gray scale was kept constant, but some flucuations may have been present due to unknown changes in the exposure settings for each individual image. The change in semi-diameter of the umbra (the blue and pink lines) is due to fore-shortening from the spherical nature of the Moon and possibly to changes in the size of the umbra during this total eclipse. (The time base on the left chart at the X axis shows midnight (UT) at 0 and on the right local time. The polynomial best fit - the black line on both charts - is a 6th order best fit).
Here is one of the Image Analyst screen captures from Souza:
Using my MS Quickbasic program (ViaX4.BAS), Fi is the computed topocentric size of the umbra (semi-diameter in degrees) and delta is the slant angle of the Earth's shadow at the plane of the Moon, both computed for the locations of Souza and Filby The best fit polynomial (6 th order) shows the true umbral semi-diameter during this total lunar eclipse as would be seen from these locations. Here some change in the size of the umbra can be seen, in particular at 0.5 and 2.3 hours and the size can be compared to the traditional constant semi-diameter of 0.65 degrees.
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