Galaxy Zoo - Amateurs Analysing Galaxies Content from the guide to life, the universe and everything

Galaxy Zoo - Amateurs Analysing Galaxies

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A spiral galaxy by Vauxhall Astra.
It's not just for fun. The human brain is actually better than a computer at pattern recognition tasks like this. Whether you spend five minutes, 15 minutes or five hours using the site, your contribution will be invaluable.
- Kevin Schawinski, astrophysicist at Oxford University, UK, one of the team who devised the Galaxy Zoo project.

In a prime example of what can be achieved by harnessing the power of the Internet, Galaxy Zoo is a research project undertaken to classify a million galaxies imaged by the Sloan Digital Sky Survey in the hopes of discovering how galaxies form. It is hoped that the results will help scientists to understand the evolution of the Universe.

Galaxies are divided into two main types, elliptical and spiral. However, it is not known how they form these shapes, and the argument about whether one type evolves into the other is as long-running as the one about whether dinosaurs were warm or cold-blooded. The Galaxy Zoo project - in displaying images of galaxies young, old and all stages in-between - should give scientists a clue as to how they develop.

Another question which hopefully will eventually be answered is whether or not the rotations of spiral galaxies are randomly distributed between clockwise and anti-clockwise. Current theories say that the formation of a galaxy is a local affair1 and that the rotation of a galaxy in one part of the sky should be independent of that of galaxies in other parts of the sky. Astronomer Professor Michael Longo from the University of Michigan has made a controversial claim that this is not the case; if he is proved right, then what cosmologists have learned so far about the evolution of the Universe is incorrect.

Setting up the Project

On 18 May, 2007, Dr Chris Lintott (co-presenter of The Sky At Night) announced that he and a team from Oxford University were undertaking a research project called Galaxy Zoo. They thought that between them they could classify 50,000 galaxies by eye. On 5 July, 2007, Lintott announced to readers of his website that some help was needed with classification. His actual words were: 'You get to be literally the first person to set eyes on parts of the Universe which surrounds us'. As if another carrot was necessary, he continued: 'If you sign up now you might just get a sneak preview'.

During a meeting, one of the team wished that they could do the rest (950,000) to complete the task. The genie who granted this wish turned out to be the BBC, who showed a clip of Lintott talking to a group of schoolchildren about the project on their BBC News 24 programme. The story on the BBC News website ranked second most-popular story on 11 July2.

Recruiting Zoo Research Assistants ('Zooites')

Is there a law of unintended consequences? Because 50,000 people registered with Galaxy Zoo within days, the team were bombarded with emails from frustrated users about how slow the site was - or couldn't get images at all. Upgrading the site so that images were available faster led to a tsunami of hits and the site crashed. Applying for (and getting) the necessary upgrades to cope with the onslaught is testament to the determination of the Galaxy Zoo team - the site was back up and running at full speed inside a few days.


[I expect] amateurs to make a better job of it than the experts. We get hung up on the details. I got stuck myself! I've found that members of public are much better; they just go with it, on first instinct. They don't get too stressed about the images. Astronomers aren't the best people to do this.
- Cosmologist Kate Land, Galaxy Zoo team member.

A new user interested in signing up for the project just needs to load the website and read the tutorial. You don't have to be a scientist or have any astronomy qualifications, just know how to recognise certain shapes. Then when you are ready to proceed, you are given 15 random galaxies to classify as:

  • Spiral
    • Clockwise
    • Anti-clockwise
    • Edge On/Unclear
  • Elliptical
  • Star/Don't Know
  • Merger

Don't worry if you don't pass the 'test' first time, it's not an exact science and your skills will improve with practice. You can retake the test as many times as necessary, and when you've scored a magic eight out of the 15, you sign up with a user name and complete the registration. Then the fun can begin! If you find anything unusual (or just not listed in the FAQ) you can send the team an email with the reference number. Due to the inundation though, don't expect a personal reply anytime soon. However, the team have promised to answer everyone 'eventually'.

I'm only half joking when I've been telling the team we're going to set up a website to invite the public to answer the queries sent in. We'll call it Email Zoo.
- Dr Chris Lintott.

The Galaxies

Spiral galaxies have a central spherical hub, with giant arms which spiral outwards to form a flat3 disc around the hub4. They rotate in a certain direction, with the arms trailing behind. Some have a straight bar across the middle, and the spiral arms come from the ends of the bar. Some spirals can be very distorted and warped, such as this example. Spiral galaxies should be classified as Clockwise (CW), Anti-clockwise (ACW) or Edge-On/Unclear.

Sometimes with an 'Edge On', the rotation can still be observed, as in this example. If the rotation is clear, it should be classified as CW or ACW, as these are the main statistics which the team are collating.

Elliptical galaxies are a collection of stars, containing any amount between 100,000 and several billion. These appear to 'bulge' and are more oval and 3D in appearance, like a rugby ball. Lenticular galaxies, (like M82), are a cross between spiral and elliptical, with lots of stellar dust giving off a halo effect. These should be classified as 'elliptical'.

Mergers - this category is pretty much self-explanatory really: anything that looks like it's interacting with something else, or is so misshapen it's the only explanation. Our local star, the Sun, takes about 225 million years to complete one orbit of our galaxy, so the last time the Earth occupied the little bit of space it's taking up now was during the Triassic Period, before even the dinosaur ancestors of T-Rex were born. On that kind of time-scale, mergers take a very long while indeed. A 'cosmic trainwreck' of two (or more) colliding galaxies can take around a billion years.

Ring galaxies are the result of a certain kind of merger - and the team want to be informed of any which happen to appear in your sessions. Since the launch of Galaxy Zoo, ring galaxies have been found to be more common than first thought.

Quantum Singularity: Yes, it's possible to 'see' a black hole, because there will be a visible jet stream. This is the Holy Grail of the team, to be flagged up by emailing them directly and alerting the Zookeepers at the Galaxy Zoo forum.


Occasionally a green, blue or red line will appear; this is a satellite orbiting the Earth which has triggered the camera - so nothing to get excited about. These should be classified as 'Star/Don't Know' so they can be removed from the database by the team.

Quasars5 are also logged by the CCD camera. Clicking on the galaxy analysis page will reveal very sharp peaks in the spectrum. These should be classed as 'Star/Don't Know'. Also, stars in our own galaxy, which completely fill the analysis page, need to be rated in this way. This is what a star in our own galaxy, (the Milky Way), looks like when zoomed out a little.

The Galaxy Zoo Forum

The official Galaxy Zoo Forum was launched on 25 July. The 'Zooites' (as the analysers have affectionately been nicknamed by the team) can start new threads, ask questions and upload pictures direct from the SDSS website. There are 'sticky' threads for 'Best Spirals', 'Most Beautiful', 'Completely Weird', 'Sexy Shapes', and 'Gotta Love Those Blues', etc. The blue irregulars, edge on spirals and cosmic trainwrecks (collisions) seem to elicit the most attention, but finding a Messier object draws much kudos from fellow Zooites.

Green Pea Galaxies

The Zooites discovered a brand new class of galaxy - the 'green pea' - which professional astronomers are now studying.

Hanny's Voorwerp

A strange green 'galaxy', discovered by Dutch schoolteacher Hanny van Arkel, was featured as Astronomy Picture of the Day on 25 June, 2008. The weird object has been named after its discoverer: Hanny's Voorwerp!

Object of the Day

Special attractions are picked by the zookeepers (as the team have been affectionately nicknamed by the Zooites) for 'Object of the Day'; it may be a planetary nebula, a warped spiral or a lenticular galaxy like M826. The green emissions are high-speed gas, and one Zooite reported that even his colour blindness didn't prevent his enjoyment of the object: at the SDSS website there are tools to play with a selected image, including 'invert' - in this case allowing the viewer to see the green gas as pink against a white background.

Twenty Million Viewings

The Galaxy Zoo project was such a success that the original plan of getting each galaxy to be classified by one person was abandoned in favour of running each image past as many people as possible. Within a month of the project launch, 80,000 Zooites had viewed and classified the one million galaxies, with each galaxy having been viewed by ten different people. As they had more than achieved their original objective in such a short space of time, the team set a new target of having each of the one million galaxies classified by 20 different Zooites.

This aimed to provide statistics indicating the reliability of the classification of those million galaxies so it can be usefully accessed by anyone from the astronomy (or other scientific) fields. The information stored will be of phenomenal value to anyone studying the subject in years, possibly decades, into the future.

The Galaxy Zoo website was awarded 'Site of the Week' status by PC Magazine on 30 July, giving it an Editor rating of 4/5. It lost a point on account of the GZ staff being unresponsive to emails7. The project featured in the August edition of the BBC's The Sky at Night programme with Sir Patrick Moore and Dr Chris Lintott. As they were demonstrating how easy the website is to use, Patrick commented on how addictive classifying galaxies can be:

You go on intending to classify ten and end up doing 20, then an hour passes before you know it!

Patrick had steadfastly refused to embrace the age of the computer, famously writing all his books on his trusty old 1908 typewriter. However Galaxy Zoo seems to have converted him and it must have amused fans of the show to watch him finally succumb to the inevitable.

The Galaxy Zoo project followed the lead of pioneers like SETI@home and 'Clickworkers' (where users could examine images broadcast from Mars). It is not known how long Galaxy Zoo will run, but they're not likely to run out of galaxies to analyse anytime soon.


The awesome beauty of some of the images has to be seen to be believed. Most participants agreed with the view of one Zooite posting about how honoured they were to be a part of the project, and what a privilege it is to be living now with this technology available. One wonders what the likes of Giordano Bruno and Jeremiah Horrocks would have thought.

Why should I leave this green-floored cell,
Roofed with blue air, in which we dwell,
Unless, outside its guarded gates,
Long, long desired, the Unearthly waits
Strangeness that moves us more than fear,
Beauty that stabs with tingling spear.

- CS Lewis.
1If the word 'local' can be applied to something spanning millions of light-years.2For the terminally curious, the top online news story was about a Best Man who got his timing a bit wrong.3Although they can be many light-years in thickness, they appear flat in comparison to their diameter.4Imagine a pancake with an orange in the middle.5A quasar is the central hub of an extremely distant galaxy.6M82 is about 12 million light-years away in the constellation Ursa Major (The Great Bear), and under suitable conditions can be viewed with a small telescope.7There is plenty of Zookeeper interaction at the GZ Forum.

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