When Chris Lintott, a researcher in the department of physics at the University of Oxford, first considered launching a Web site to ask the public to help classify photographs of 1 million galaxies, he assumed it would probably take three or four years to complete.
Galaxy Zoo, (galaxyzoo.org) launched in July 2007, was supposed to be a side project; instead it has turned into the biggest citizen-science experiment on the Web.
Galaxies can be classified as spiral, elliptical or merging (when two come together). The Sloan Digital Sky Survey, or SDSS (www.sdss.org), has images of nearly 1 million galaxies; what those images don’t have in their raw form is the information about what class of galaxy is pictured.
Lintott had hoped that each image would get 10 classifications, or “clicks,” and that the public would prove able to classify galaxies accurately according to their features. Three weeks and 10 million clicks later, he was proved right: the public is capable of classifying galaxies as well as, or even better than, professional astronomers.
And quickly, too.
“It was like being hit by a tidal wave,” Lintott said.
The images have now had more than 70 million clicks in total, allowing Lintott and his team to go beyond simply sorting galaxies into spiral, elliptical or merging categories.
“You can have confidence, as we can say, ‘100 percent of people think that’s a spiral galaxy, so it’s really, really spirally,’” Lintott said.
His team was allocated precious time on the IRAM 30m radio telescope in southern Spain, and was easily able to select just 40 galaxies from the original sample to study, safe in the knowledge that the scientists had exactly what they needed.
After Galaxy Zoo’s initial success, Lintott wanted to take a closer look at merging galaxies. At 5pm one Tuesday, he posted a spreadsheet listing a selection to the forums and asked members to take a look and e-mail him the best. Then he went to the pub.
One “Zooite,” Richard Proctor, a telecoms consultant, spotted the spreadsheet and thought: “I can build a Web page to do that!”
By the time Lintott logged back in, the Web interface was already in use.
“What was going to be a quick little study turned into a much larger study of about 45,000 images,” Proctor said.
Each image has now had more than 25 clicks, with four particularly committed souls having seen every single one. The first academic paper about those merging galaxies has been submitted, and Proctor is listed as a co-author.
It’s not the first time collaborative astronomy has proved a hit online. The Search for Extraterrestrial Intelligence (SETI) project created the most powerful distributed computer ever with its SETI@home project launched in May 1999, which used spare processing power on home computers to process data collected from a specific wavelength to see if aliens were trying to get in touch.
It was used by 5.2 million people and offered, at its peak, 265 teraflops (1 trillion calculations a second) of processing power.
Similarly, NASA’s Clickworkers project in 2000 to 2001, found that ordinary people were just as good as astronomers at identifying craters on Mars in photos.
The biggest influence on Galaxy Zoo, however, was Stardust@home, where users search for tiny interstellar dust particles within images returned by the 2006 Stardust mission. Thousands of users have logged on to the site.