Point a powerful telescope in almost any direction in the night sky and you will see galaxies. An awful lot of them. There are so many, in fact, that the million galaxies detected and photographed by the Sloan Digital Sky Survey (2000-08) probably represent no more than one thousandth of one percent of the galaxies that actually exist.
The survey, which used a robotic telescope in New Mexico, has released vast quantities of data into the public arena, and the next task is to make sense of that data. That is where Galaxy Zoo comes in.
The idea is to classify the images of the galaxies so that an idea can be obtained of how the various types are distributed, and any patterns can be detected. This is a huge task for the relatively small number of professional astronomers there are in the world, so help was sought from a vast army of amateur enthusiasts who can at the very least tell a spiral galaxy from an elliptical one. Thanks to the World Wide Web, the task of classifying a million galaxies is not so difficult after all.
Galaxy Zoo was set up in 2007, on a completely non-commercial basis, by a group of astronomers who were mostly at UK universities. The plan was to present the volunteers with images of galaxies and ask for their opinions on whether they were elliptical or spiral and, if the latter, whether the galaxy was turning clockwise or anti-clockwise. They wanted multiple classifications for each galaxy, because the proportion of people who reckon that a galaxy is a spiral is important information in its own right. With many galaxies, it is not clear what shape they are, maybe because the image is indistinct or perhaps because it only shows an edge-on view to us.
The website owners reckoned that the task would take about two years to complete, but they were amazed by the response they got. Within the first day they were getting more than 70,000 classifications an hour, and they reckon that the first year delivered more than 50 million classifications from more than 150,000 volunteers.
Many of the images had not been seen by anyone before they were offered to the volunteers, and there were surprises in store. The most notable of these was a blue blob on one image that was queried by a Dutch volunteer, a schoolteacher named Hanny. This has now become known as "Hanny's voorwerp", which is Dutch for "object". This has since become the subject of more detailed observations.
The success of the project is undoubted, with the team of astronomers freely admitting that the amateurs have often produced better classifications than the professionals. The information gained has been used to make a number of new statements about galaxies, such as that neighboring spirals tend to spin in the same direction, and that up to a third of red galaxies are spirals, whereas it had previously been thought that they were nearly all ellipticals. The world's telescopes are now being focused on a host of objects that appear to have features of interest as noted by the volunteers.
The project has therefore now moved to its second phase, which is to look more closely at a smaller set of galaxies (a quarter of a million) and ask the volunteers to make more decisions about each image. Questions being asked include the shape of the galaxy (i.e. how rounded it is), whether an edge-on galaxy has a rounded or boxy-shaped bulge at its center, how tightly bound the arms of a spiral are, how many arms there are (this is no means always easy to determine), how prominent a central bulge is, and whether there are any odd or unusual features. Volunteers will sometimes be asked to compare two galaxies and say which one shows a particular feature to a greater degree.
Becoming a volunteer is not difficult, and mainly involves taking a short test to show that the volunteer's opinions are generally in line with those of the majority. There is a simple tutorial for anyone who is not sure if they want to take part, but would like to test their opinions anonymously against the expert view. The website includes a Forum and a Blog so that discoveries can be shared and discussed.
Galaxy Zoo is an excellent example of how ordinary people can make a real and valuable contribution to science, as well as enabling people to see pictures of some wonderful objects that very few people have ever seen before.