John Vallerga polishing a mirror that will be mounted atop one of the towers of the Golden Gate Bridge (Robert Sanders photo)
In celebration of the 75th birthday of the Golden Gate Bridge, space scientists at the University of California, Berkeley, are topping each tower with a glittering solar candle.
The “candles” are mirrors that the public can control through the Internet to make them swivel and tilt, flashing a glint of reflected sun like a lit candle.
"We’re lighting the birthday candles at the bridge," said John Vallerga, a researcher at UC Berkeley’s Space Sciences Laboratory (SSL), who conceived the project. Normally, he builds instruments that fly aboard spacecraft such as the Hubble Space Telescope.
His Earth-bound project, Solar Beacon, is one of 75 birthday tributes approved by the Golden Gate Bridge District in celebration of the bridge’s completion in 1937, and one of the few approved for installation on the bridge itself.
"This is not something we have ever done before or will ever do again - we don’t let people place art on the bridge," said bridge manager and mechanical engineer Kary Witt. "But this is a pretty cool project, especially the technology they’re using, which is based on what they use in space."
The mirrors, or heliostats, will be mounted by a member of the SSL team on the tops of the two towers on Friday, May 25, and hopefully be operating in time for the bridge’s huge birthday bash on Sunday, May 27. The UC Berkeley team, all volunteers who raised money for the project through private donations and received seed funding from SSL, hope to flash the mirrors at the assembled crowds on Crissy Field along the San Francisco waterfront during Sunday’s celebrations.
"We’re presenting a big fireworks display and light show on the 27th, and Solar Beacon extends that symbolism of light into the daytime," Witt said.
Space scientists from SSL’s Center for Science Education will also set up a booth at a Future Fair being held from 11 a.m. to 7 p.m. at Crissy Field Center. The booth will offer hands-on solar and satellite-building activities and information about the sun’s magnetic field. The scientists will answer questions about the heliostats and careers in science and engineering - in particular, careers in building satellites, "our bridges to space," according to science center director Laura Peticolas. Internet-connected heliostats
Vallerga and his colleagues see the bridge every day from their perch in the Berkeley hills and the sun’s reflection off plate-glass windows and buildings miles away throughout the Bay Area.
"I wanted people to notice these solar reflections and glints all around us all day long," he said.
Each heliostat is about two feet across and consists of four six-inch-square mirrors. The mirror assembly is attached to motors that can swivel and tilt to send a reflected image of the sun anywhere within view of the tops of the orange towers. Through a website, http://solarbeacon.org , members of the public can go online and schedule a time when both of the heliostats will swivel into position to flash the sun directly to their location. Commands will be relayed to the heliostats via a cellular modem.
Though the public can now go to the website to test the scheduling software, they cannot yet schedule viewings. Vallerga suggested that people check the website periodically, starting May 27, to catch the site when it goes live and schedule a light show.
The image of the sun is about 1/2 degree across, which means it will be magnified to more than 90 feet at a distance of about two miles. People will see a bright point of light on the top of each tower, similar in brightness to the sun reflecting off a car mirror, for about 30 seconds.
Astrophysicist Pat Jelinsky wrote the computer software that takes a person’s location (latitude, longitude and altitude), calculates the position of the sun at the time specified, and determines how to orient the heliostat to reflect the sun to the right location at the right time. The public can even program the mirror to wink on and off.
"The point is to transform the light and draw attention to the bridge," Vallerga said, "but I think it’s just a cool idea."
The heliostats, encased in frames cut to resemble the profile of the Golden Gate Bridge towers, will remain in place until Aug. 30, allowing about three months for the public to play with it. The engineering team had to build the heliostats to withstand 100 mile-per-hour winds and salty fog, and Vallerga expects to have to climb the two towers a few times to clean the mirrors.
Vallerga hopes the project will create enough interest to resurrect another of his art projects, the installation of five prism heliostats along a mountain ridge to convert sunlight into refracted rainbow colors. Conceived with London-based artist Liliane Lijn, the plan to place the spectro-heliostats on Mt. Sainte Victoire in France in 2013 was recently put on hold for lack of funds.
Collaborating at UC Berkeley with Vallerga, Lijn, Jelinsky and Peticolas are detector scientists Jason McPhate and Adrian Martin; mechanical engineers Greg Dalton, Joe Tedesco, Chris Scholz and Greg Johnson; system administrator Robert Lettieri; and science educators Ruth Paglierani, Dan Zevin and Kyle Fricke.