Galaxy Zoo

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= Citizen Science project in astronomy, part of the Zooniverse



1. Dave Munger:

"Galaxy Zoo is an effort to classify about 250,000 galaxies that were imaged by the Sloan Digital Sky Survey over the past eight years. Once I created an account, I was immediately presented with a stunning image of a galaxy and asked to decide whether it was a “smooth” galaxy devoid of apparent structure or a “featured” galaxy with topological characteristics like spirals or bars. Having never done this, I wasn’t exactly sure how to proceed, but help pages were readily available. After checking the help page, I clicked “smooth.”

Next I was asked if the galaxy was round, cigar-shaped, or somewhere in between. I clicked “in between,” and the next screen asked if there was anything odd about this galaxy. Although it seemed odd indeed that I was being trusted to do this important work, I clicked “no” and moved on to the next galaxy. Within a few minutes, I had classified a half-dozen galaxies—not a bad contribution to science for someone whose only astronomical experience was an “intro to astrophysics” course taken over 20 years ago as a college freshman!

But how does a project like Galaxy Zoo ensure that participants aren’t taking shortcuts or fudging data? Alexander Bastidas Fry, a graduate student in astronomy at the University of Washington, explains how the site works on his blog The Astronomist. Since participants must register with the site, it’s possible to track their classifications and compare them to the work of others. Each galaxy is classified many times, and the work of long-established, accurate contributors is compared to newbies. Unreliable users’ classifications are weighted lower, while more consistent users earn a higher weight. The results are statistically more accurate than those obtained from professional astronomers—even though the experts in the field rarely use their limited time to classify a quarter-million galaxies." (

2. By Jeffrey R. Young:

"a Web site that invites anyone to help categorize images from the Sloan Digital Sky Survey.

It's called Galaxy Zoo, and it's led by Chris Lintott, an astronomer at the University of Oxford.

Just click "classify galaxies" on the Galaxy Zoo Web site, and a picture from a telescope appears, along with questions including "Is the galaxy smooth and rounded?" and "Does the galaxy have a mostly clumpy appearance?" Visitors must register and complete a short tutorial before their results are counted. Each image is shown to at least 10 different people to try to cut down on erroneous classifications. If 80 percent of the crowd agrees on a classification of an image, it sticks. Otherwise, the image might go through the whole process again.

"It's not some fun game online while the scientist do the real work," says Mr. Lintott. "I hope visitors are learning that science is not just something done by people in lab coats in some underground bunkers. Science is something people can get involved in."

The number of volunteers surprised the organizers. "The server caught fire a couple of hours after we opened it" in July 2007, he said, burning out from overuse. More than 270,000 people have signed up to classify galaxies so far.

One of them is Hanny van Arkel, a schoolteacher in Holland, who found out about the site after her favorite musician, Brian May, guitarist for the rock group Queen, wrote about it on his blog.

After clicking around on Galaxy Zoo for a while one summer, she landed on an image with what she describes as a "very bright blue spot" on it. "I read the tutorial and there was nothing about a blue spot," she says, so she posted a note to the site's forums. "I was just really wondering, What is this?"

Her curiosity paid off.

Scientists now believe the spot is a highly unusual gas cloud that could help explain the life cycle of quasars. The Hubble telescope was recently pointed at the object, now nicknamed "Hanny's Voorwerp," the Dutch word for object.

Astronomers have published papers about the discovery, listing Ms. van Arkel as a co-author. "Don't ask me to explain them to you, but I am a co-author of them," she says with a laugh.

Now other disciplines have approached Galaxy Zoo to find out how they can use the approach." (