Deep Sky visual observing requires very dark skies, far away from city lights. I live in San Jose, California, in the heart of Silicon Valley. One might think I need to drive long distances to find friendlier skies, but fortunately, the situation is not that bad. Here are some of my favorite observing sites around the south bay.
Henry Coe State Park
Description: State park near Morgan Hill
Elevation: 2600 ft
Latitude: N37 11.250
Longitude: W121 33.016
This site is only a 45 minute drive away from my house, although the road is pretty narrow and sinuous for the last 10 miles. The light pollution is pretty bad, especially from the north east to the south east, so I only go to Henry Coe in summer to observe star clusters, and nebulae using a narrow band filter. If you get lucky, the fog sometimes rolls in and covers the cities to the north and the east. In those rare cases, it can get pretty dark up there.
Description: Parking lot adjacent to the San Luis Reservoir.
Elevation: 648 ft
Latitude: N37 03.90
Longitude: W121 10.217
This is my favorite observing site because it is fairly dark (SQM 21.4 on good nights) and is only an easy 50 minute drive away from my house. The only conspicuous light domes are to the east and the north west. This site is for winter observing only (including late fall and early spring) The winds are pretty strong during the rest of the year.
Description: Private observatory located off of Little Panoche Road, near Mercey Hot Springs
Elevation: 1400 ft
Latitude: N36 42.4800
Longitude: W120 51.08
This is one of my favorite observing sites. It is an easy 2 hour drive away from my house, and is a truly dark site (SQM 21.8 on good nights) I go there every opportunity I get!
Lake San Antonio
Description: A county park and reservoir, site of the annual CalStar star party.
Elevation: 1000 ft
Latitude: N35 49.22
Longitude: W120 57.50
This site is the darkest of local sites, but it takes almost 3 hours to get there. Mostly for spring and fall galaxy observing. It gets beastly hot in summer, and pretty cold in winter. It is also occasionally susceptible to fog.
Description: Private property on which the Golden State Star Party is held.
Elevation: 4400 ft
Lat: N41 8.06221
Lon: W120 580675
Located near the small town of Adin, in northern California. I’ve heard it was about as dark as it gets. Since I plan to go to GSSP this year, I will report back on the quality of this site later this summer.