I've seen the effect your describing in Clavius...
Orion

"kandr" wrote in message
...
I got up around 2:30 EDT on Wed 8/20 to have a look at Mars. Seeing
was unremarkable and when Mars finally set around 3:30 (behind my
neighbor's rooftop) I turned the 10" lx200gps toward the Moon.

I guess I haven't been observing very long because I still always find
it fascinating to scan the lunar surface. I consider it a natural
wonder. With a telescope it's like having the Grand Canyon in your
backyard to look at whenever you want.

Anyway, while travelling down the terminator I noticed a thin
triangular wedge along the floor of Archimedes, extending from near
center and broadening toward the eastern side of the crater: a beam of
sunlight poking through a pass in the western wall had painted a slice
of light on the floor of the crater and splashed up against the
opposite inside wall.

It even appeared to me that the slice was slightly hooked toward the
north, but now I am doubting this. Would one be able to see the
curvature of the lunar surface over the short distance of Archimedes'
radius? If you have observing experience with this (or can do the
math) I'd like to hear.

--
kandr



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