While watching the fat moon rise an hour before sunset yesterday, (18* N. LAT)
I commented to a sailor friend that a full moon and the sun cannot be simultaneously visible-
From anywhere on the earths surface.
He bet me five bucks and said he'd seen it happen at mid north lat. around 45* in summer

I've looked but can't find a reference re this (to me)
impossible sight.

Help needed with explaination please....cc

I don't think you're wrong at all. To my knowledge, you can never see a full moon during the daytime since it rises at sunset and sets at sunrise. I can't think of any circumstance where this wouldn't be the case anywhere on the earth's surface. The moon can certainly 'appear' to be full though when it technically isn't... perhaps that is what your friend saw.

Dig

Thanks for your reply
After further searching I found this-

According to Cornell Astronomer Jagaheep D. Pandian this sight is visible near 66.5* North-
Very rarely but sometimes-

Pandian explains it here

I shall nonetheless demand payment of $5 on the basis that my sailor friend was not looking at a full moon-
But then I'm sure he will demand I buy him a beer for saying 'impossible'
...cc