Some believe Stonehenge was built as a massive analog computer to forecast coming eclipses, in essence a very long-term clock. But to maintain accuracy, the great stones would need resetting about once every 300 years. More locally, the Long Now Foundation (a group dedicated to long-term thinking) has created the Orrery, an elegant heliocentric model that shows the position of the planets visible to the human eye. It's the "planetary display" for another Long Now project called the 10,000-Year Clock. The foundation hopes our very distant descendants will recognize their sky, and better understand our clock. As with Stonehenge, the difficulty is accuracy: To this end, the "Solar Synchronizer" corrects drift, harmonizing the clock with solar noon and accounting for a 15-minute differential between solar and absolute time. Its not as pretty as the Orrery, but its crucial, especially if the Earth were to experience a meteor impact, intense volcanic eruptions, or worse. Stunning working prototypes of the Orrery and the Solar Synchronizer are on view at the Long Now Museum and Store during the Mechanicrawl, a self-guided walking tour of mechanical marvels. To truly appreciate the long now, take a long walk (grab a crawl map and expect lots of special exhibitions) through the dreaded Fisherman's Wharf area. Admirable machinery of the past much of it usually unavailable to the public includes the highly complex mechanical computer sitting aboard the USS Pampanito submarine and turn-of-the-20th-century automatons at the Musée Mécanique.
Sat., July 12, 3 p.m., 2008