Is 10 percent of the side facing us lit 10 percent of the way between new and Full Moon?

No because the Moon is a spherical surface and the rate at which the area changes with time is related to the projected area on the sky as a function of time. The lunar phase is related to the cosine of ( T/29.5d), which does not vary uniformly in time throughout the synodic lunar month.


Copyright 1997 Dr. Sten Odenwald

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