Though not as dramatic as the solar eclipse two weeks ago, the planet Venus transit across the sun today is a far rarer event, not occurring again for another 105 years. The transit begins today locally at 3:06pm and is viewable until sundown. You can either build a special viewing box or buy a pair of welding glasses from your local hardware store to watch the transit without permanently damaging your eyes (which happens when you look directly into the sun for too long).
Another option is to visit one of 17 sites in the Bay Area equipped with special viewing equipment. In San Francisco, drop by Ocean Beach across from the Beach Chalet where the San Francisco Amateur Astronomy club will be set up with a six-inch reflector with a protective sun filter. In Berkeley, the Lawrence Hall of Science on campus will have solar telescopes on their main plaza, with additional events inside after 5pm.
To find a viewing station nearest you, check out this list: https://sites.google.com/site/aancsite/calendar/pre2010/2012-events. Or you can view the transit from the comfort of your home computer at the Exploratorium’s live webcast here: http://www.exploratorium.edu/venus/.