I would drive to the Hancock Overlook on the Kanc. I’ve gone there several times. It’s a pretty spot on moonlit nights, and very dark on moonless nights, but easy to get to. I’ve taken my small telescope there a few times in the past, but there is an active amateur astronomy community in NH, so search that out. You son could look though some of these folks high end scopes and he might get hooked on astronomy. I did as a kid…