At the top of Mt. Diablo they have those pay-per-view telescopes so you can view things a bit closer. It was a bit hazy that day, so I didn’t try it out.
I think the best time to go is in the winter when the skies are clear and you can see the Sierras. My next mission regarding this mountain is to go up at sunrise to catch the light over the valley and then to catch the sunset. Unfortunately you can only get up so far since they don’t open the gate until sunrise but I scouted a few places I could go in front of the gate. The only other way is to camp there….and that’s not happening anytime soon! lol