Not open to non-professionals after dark except for a handful of "Photo Nights" each summer. If you drive up there after dark, you'll get yelled at (at a minimum) or they'll call the cops on you for trespassing.
True enough, but headlights driving up the mountain cause light pollution for the astronomers working at the observatory (who necessarily need to work at night).
"Please do not visit the observatory at night without a ticket to one of our evening programs.
Lick Observatory is an active research facility, and at night all of the buildings are locked and astronomers are working at the darkened telescopes. Telescopes require the darkest possible conditions to detect the faint light from celestial objects. The success of our work relies upon minimizing lights around the observatory at night. Thank you."
