How many arms does a spiral galaxy have? Can you spot a galaxy with a central “peanut” bulge? How about a galactic merger? You won't need a towel to write an astronomical 'Hitchhiker’s Guide to the Galaxy', just a computer. Answers to these and other strange questions will be provided by worldwide web users in an online citizen science project called Galaxy Zoo 2, which launches today.The new initiative is a follow-up to the highly successful Galaxy Zoo project that enabled members of the public to take part in astronomy research online. By working together, they proved to be just as good at spotting galaxies as professional astronomers. But whereas the original site only asked users to identify whether a galaxy’s shape was spiral or elliptical, and which way it was rotating, Galaxy Zoo 2 asks them to delve deeper into 250,000 of the brightest and best galaxies to search for the strange and unusual.“The first Galaxy Zoo provided us with a rough guide to the sky and now we want our users to fill in all the details and create a real Hitchhiker’s Guide to the Galaxies,” said Chris Lintott of Oxford University, one of the founders of Galaxy Zoo.Astronomers came up with the idea of involving online volunteers because the human brain is better at pattern recognition than a computer. What they didn’t expect was the huge enthusiasm for the project. In the 18 months since Galaxy Zoo’s initial launch, more than 150,000 armchair astronomers from all over the world have made 80 million classifications of one million galaxies.Kevin Schawinski of Yale University, another of Galaxy Zoo’s founders, said, “The response from the public was absolutely overwhelming. With their help, we’ve been able to learn a lot about how galaxies evolve and how they relate to their environment. With the detail from Zoo 2, we'll be able to discover even more about how galaxies work.”Steven Bamford of the University of Nottingham said, “Galaxy Zoo has given everyone with a computer an opportunity to contribute to real scientific research. We want people to feel truly involved in the project and keep them up to date with what we’re doing with the results they’re generating.”As with the original site, people are free to look at and describe as many galaxies as they like – even five minutes of work provides a valuable contribution, according to the site’s founders. Galaxy Zoo 2 is intended to be even more fun as galaxies are pitted against each other in “Galaxy Wars” (over such questions as “which one is more spiral shaped?”), and users can compete against their friends to describe more objects as well as record their best finds.Proof that unusual discoveries can be made is the catalogue of merging galaxies provided by users – more than 3000 of these rare cosmic pile-ups have been caught in the act by Galaxy Zoo users. The team has already used the IRAM radio telescope in Spain’s Sierra Nevada to follow up the most exciting mergers, and are asking for more examples to study.“In this International Year of Astronomy, it’s great to have so many people looking at these beautiful images of galaxies from the Sloan Digital Sky Survey,” said Bob Nichol of the University of Portsmouth, spokesperson of the SDSS-III project and member of the original Galaxy Zoo team. “No single professional astronomer has ever looked at all these images and sometimes astronomers miss the wonder of what they are. I think the public gets this better than us.”The Galaxy Zoo team is led by scientists from the University of Oxford, the University of Nottingham, the University of Portsmouth, Yale University, Johns Hopkins University, UC Berkley, and Fingerprint Digital Media of Belfast. The development of Galaxy Zoo 2 was funded by The Leverhulme Trust, and a grant from Microsoft.The digital images used in Galaxy Zoo were taken using the robotic Sloan Digital Sky Survey telescope in New Mexico. For more on the Sloan Digital Sky Survey visit www.sdss.org The Galaxy Zoo 2 website is www.galaxyzoo.org