August 8, 2007

The Galaxy Zoo welcomes a flood of visitors

A new scientific project, called the Galaxy Zoo, is celebrating the enrollment of its first 85,000 participants, exploring the distant Universe via the Internet.

The goal of the project is to classify images of one million galaxies from the Sloan Digital Sky Survey (SDSS-II), with the help of the general public.

The Galaxy Zoo opened its online gates in mid-July. "The response has been breathtaking," said Alex Szalay from Johns Hopkins University, a member of the Galaxy Zoo team. "The traffic was 20 times higher than what we hoped for. This shows the public is really interested in science if they feel they can contribute in a meaningful way."

Galaxies come in two main categories, explained team member Daniel Thomas of Portsmouth University. In spiral galaxies, like the Milky Way, most stars follow circular orbits and move in the same direction, giving the galaxy a flattened, frisbee-like shape. In elliptical galaxies, on the other hand, stars move on randomly oriented, elongated paths, so the galaxy as a whole has a football-like shape.

Visitors to the Galaxy Zoo take a short online tutorial then sort galaxy images into these categories. "Computers can do this classification automatically, but humans are far more accurate," said Thomas. "It's like trying to distinguish male and female faces -- no computer algorithm will do this as accurately as a person, because we are much better at identifying the most important cues."

But giving individual attention to a million galaxies takes many pairs of eyes, especially as every galaxy must be classified by multiple people to ensure reliability.

Working around the clock, the Galaxy Zoo team made its website fast enough for the flood of participants, explained a tired Jan Vandenberg of Johns Hopkins. "The demand on the first day was so great, we blew a circuit breaker in our computer room!"

The team upgraded their computer hardware, simply to keep ahead of public demand. According to Szalay and Vandenberg, Galaxy Zoo users have already submitted over 12 million galaxy classifications. At its peak, the Galaxy Zoo served up more than 60,000 galaxies an hour to users around the globe.

"We now have the world's largest computer working for us, through the combined power of all these human brains," commented Thomas.

"We wanted to create an intriguing yet intuitive web site," said Galaxy Zoo site designer Phil Murray, "so that anyone, from around the globe, would enjoy coming back time and time again to take part. It helps that the galaxies themselves are such beautiful and evocative objects."

As with any zoo, the oddest animals provide much of the fun. The Galaxy Zoo team has received thousands of emails from those who want to share their latest discovery. "It's very rewarding to hear from someone who has found a particularly beautiful image, or has a question about a set of merging galaxies they've observed," said Chris Lintott from the University of Oxford. "We've had complaints that the site is addictive, as you never quite know what the next image is going to reveal!"

"We want our catalogue to be the most accurate, as well as the largest," explained Oxford astronomer Anze Slosar. "To do that we need to have several people classify each galaxy. There's plenty out there for everyone, and the next galaxy is always difficult to resist."

The underlying science goal, explained Slozar, is to understand how spiral and elliptical galaxies form. "We have theories for how this happens, but to test them we need to know what kinds of galaxies are found in different cosmic environments. The combination of SDSS-II and the Galaxy Zoo will give just the information we need."

Already hard at work analyzing their data, the team hopes to welcome more visitors through the gates of the world's newest - and most unusual - zoo.

The Galaxy Zoo is open for business at

About Sloan Digital Sky Survey

The Sloan Digital Sky Survey (SDSS-II) is the most ambitious astronomical survey ever undertaken. When completed, it will provide detailed optical images covering more than a quarter of the sky, and a 3-dimensional map of millions of galaxies and quasars. The data are released to the scientific community and the general public in annual increments

Funding for the SDSS-II has been provided by the Alfred P. Sloan Foundation, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, the Max Planck Society and the Higher Education Funding Council for England.

The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions: the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, Cambridge University, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPA), the Max-Planck-Institute for Astrophysics (MPIA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.

Notes to editors

  1. The Galaxy Zoo project is a collaboration between researchers at Oxford University and Portsmouth University in the UK and Johns Hopkins University in the US using data from SDSS-II. The site was developed by Fingerprint Digital Media of Belfast.
  2. Images related to the project can be downloaded from
  3. For more details on the Sloan Digital Sky Survey go to For full details of those involved go to


  • Alex Szalay, Johns Hopkins University, 410-516-7217,
  • Chris Lintott, University of Oxford, +44 (0) 1865 273638,
  • Daniel Thomas, University of Portsmouth, +44 (0) 23 9284 5171,
  • Gary S. Ruderman, Public Information Officer, Sloan Digital Sky Survey 312-320-4794,