In 1968, John Dobson started the San Francisco Sidewalk Astronomers with the help of two boys who loved astronomy but couldn’t join an amateur astronomy club in the city because they were too young. So the trio created their own club, carting two homemade telescopes onto Jackson and Broderick Streets and inviting curious passersby to take a look at the craters of the moon, the rings of Saturn, the banded clouds of Jupiter.
Forty years later, the San Francisco Sidewalk Astronomers is still going strong, boasting a web site replete with a monthly star chart, specific for San Francisco, a calendar of monthly amateur astronomy events, a helpful "cheat sheet" of astronomical facts and answers to questions that routinely come up if you set up a telescope on your neighborhood sidewalk, and where to go if you want to borrow, build or donate a telescope.
Another great resource for the budding SF amateur astronomer is the Randall Museum, which hosts star parties, lectures by amateur and professional astronomers and classes for making your own Dobsonian telescope from scratch. The free public lectures at the Randall Museum take place on the third Wednesday of each month, sponsored by the San Francisco Amateur Astronomers.
Since 1952, the San Francisco Amateur Astronomers have been an invaluable resource for stargazers to learn about the choicest observing sites throughout the Bay Area, monthly star parties and make contact with a community of like-minded folks. Be sure to also check out their astrophotography web page, where they have uploaded photos and even videos shot with their telescopes of galaxies, comets, moons, planets and nebulae.
If you can't get enough of amateur astronomy clubs in the Bay Area, check out the Astronomical Society of the Pacific and the Astronomical Association of Northern California. The Astronomical Society of the Pacific, founded in the 19th century, has members from 70 countries and claims to be the largest astronomy society in the world. It also boasts educational outreach programs, such as Astronomy from the Ground Up, a National Science Foundation-funded program that helps informal science educators such as docents and volunteers by giving them the tools and training to more effectively communicate astronomy information to the public.