I have made four colour maps now in B-V on four different nights.
The nights are arranged like this:
A uniform scale is used for all four images, from B-V = 0.0 to 1.4. The BS light is coming out in all four images around B-V=1.0, and the ES at around B-V = 0.6-0.8,
depending on whether one is looking at highlands or lowlands (lowlands are redder).
The cause of the black dips along the BS rim is the problem that the B images are slightly larger than the V images – so even with good registration of the center of the moon (to the closet pixel), there are issues in producing these colour maps. The falloff in the halo light cannot be the same power law in V and B, because the halo changes colour — but this is still to be checked.
Flat fields: tried applying the flat fields generated by Henriette on night JD2455827 (i.e., not the night of image observation!). The difference in resulting B-V values across the DS is negligible seen visually in histogram equalized images. Should be redone numerically.
Radii: The B and V image radii for 2455945.1760145MOON_B and 2455945.1776847MOON_V differ slightly: The MEASURED radii differ by 0.4 pixels while the radii determined by the time of observation and a formula differ by 0.01 pixels. The observed difference in radii probably comes from different focus – since the focal length of the system changes with focus. Also, if the focus is not equally good in the two images the apparent radius will differ, for similar reasons as well as for reasons havingto do with how the radius is measured from the images.
Super job this! Very little gradient in color on DS for most!