Looking for an outdoor activity this weekend? Check out the Exploratorium's new (free) outdoor annex! Last week, they opened 20 new exhibits and piees of artwork on the waterfront at Fort Mason (look between the Aquatic Park and the Marina district).
There's a bridge thermometer, which has a calibrated spotting scope, mounted on an Upper Fort Mason trail and trained on the Golden Gate Bridge. It allows you to see how much the span moves up and down as the structure contracts and expands in reaction to temperature changes (it can rise and fall by as much as 16 feet).
Look for the pier piling pivot, where you can see the plant and animal life living in this part of the shoreline. And learn about thermal optics from the architectural mirage exhibit.
The interior Exploratorium isn't far away - so put that on your list to visit too!