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Galaxy Zoo 2 Tutorial

Your job is very simple! When classifying you will be shown an image of a galaxy and be asked a series of questions about it. All you need to do is to look for features that mark out different types of galaxy and answer the questions as well as you can. This is a job that humans are much better at than computers, so most of the questions should be fairly easy. If you find it hard to decide upon the answer to a particular question, don't worry! There often won't be a 'correct' answer. Just pick the one that seems best and move on to the next question. By looking at all the answers given for each galaxy the Galaxy Zoo scientists will be able to work out which is most likely to be the right one, and how sure we can be about it. Your individual opinion is extremely important to making that possible.

Below is an explanation of each question, along with a selection of examples which you can use to learn and practice your classifying skills. You should try to understand why we have decided on the answers given for each example. Remember though, there isn't always a clearly correct answer, so don't worry if you occasionally find you would have answered differently. When you've read this tutorial and are feeling confident about your classifying abilities, then you'll be ready to contribute to Galaxy Zoo science!

The questions you see for each galaxy will depend on your answers to the previous questions. We try to avoid asking questions which you can't answer. You can go back if you want to change your mind, but don't spend too much time worrying about any single question or galaxy.

Q: Is the galaxy simply smooth and rounded, with no sign of a disk?

For most of the questions we want you to concentrate on the galaxy which is right in the middle of the picture. If the galaxy has just a smooth shape, often which gets brighter towards the middle, you should click Smooth. If you can see anything other than a smooth shape, for example a pattern, bar or distortion, then choose the Features or disk option here. Sometimes there are no obvious features, but the galaxy looks like it must be a flat disk. This might be because it appears very thin, or because it seems to have a well-defined edge, rather than becoming gradually fuzzier the further from the centre you look. In this case you should also choose Features or disk.

Have a go yourself… click on the galaxy images below to find out what we think the answer should be for each one.

from the centre you look. In this case you should also choose Features or disk.

Smooth	Features or disk	Star or artifact	Features or disk	Features or disk
Features or disk	Features or disk	Smooth	Star or artifact	Smooth

Q: How rounded is it?

If the galaxy is smooth and rounded, exactly how rounded does it appear? Is it more or less Completely round, very flattened and 'Cigar shaped', or somewhere In between?

Why not have a go yourself… click on the galaxy images below to see our answers.

In between	In between	In between	Cigar shaped	Completely round
In between	Cigar shaped	Completely round	Cigar shaped	Completely round
In between	Completely round	Completely round	Cigar shaped	Cigar shaped

Q: Could this be a disk viewed edge-on?

How a galaxy appears depends on the angle we look at it. When we look at a disk galaxy from the side, the disk appears as a thin line. This may be all there is, it may have a bulge in the middle, or the disk might be embedded in some larger fuzziness. If the galaxy isn't very thin, or you can see spiral arms, then the disk isn't edge on and you should choose No.

Have a go… click on the galaxy images below.

Yes	Yes	No	No	Yes
No	Yes	No	No	Yes

Q: Does the galaxy have a bulge at its centre? If so, what shape?

There is often a bulge of stars at the centre of a disk galaxy. If your answers to previous questions have indicated that the galaxy is an edge-on disk we would like to know about its bulge. Most bulges appear roughly round in shape. However, if you notice a bulge that appears square or rectangular, then please click Boxy. These are often rather subtle! If you don't see any bulge, then answer No Bulge, otherwise click Rounded.

Have a go… click on the galaxy images below to see our answers.

Boxy	Rounded	Rounded	No Bulge	No Bulge
Rounded	Boxy	No Bulge	Rounded	Boxy

Q: Is there any sign of a spiral arm pattern?

A straightforward question — no matter how many arms there are, or how obvious they are, if you can see them then click the Spiral button

Why not have a go… click on the galaxy images below.

Spiral	No Spiral	No Spiral	No Spiral	Spiral
Spiral	Spiral	Spiral	No Spiral	No Spiral

Q: How tightly wound do the spiral arms appear?

This question is a little tricky. Do the spiral arms wrap Tight around the galaxy's nucleus, or are they Loose; or perhaps some Medium between the two?

Try clicking on the galaxy images below to get an idea of what we mean.

Loose	Loose	Tight	Tight	Loose
Medium	Loose	Tight	Tight	Medium
Medium	Medium	Tight	Medium	Loose

Q: How many spiral arms are there?

Spiral galaxies come with various numbers of spiral arms. How many distinct arms can you see? The correct answer is often not very clear — spiral arms can be messy, so a little imagination helps. If you're uncertain, say between 2 or 3, just give your best guess. If you can see there are spiral arms, but you really Can't tell how many, then you have the option of saying so.

en, tutorial, task_11, intro_3

Can't tell	More than 4	1	1	More than 4
2	Can't tell	2	4	2
3	Can't tell	More than 4	1	4

Q: Is there a sign of a bar feature through the centre of the galaxy?

Some galaxies have a straight, often fairly short, bar at their centre. For spirals, the arms will sometimes start from the end of the bar. Only answer Bar here if you see a bar feature, not just a rounded bulge.

Try to work out which of the galaxies below has a bar… click on the images to see our opinion.

No Bar	No Bar	Bar	No Bar	Bar
Bar	No Bar	Bar	No Bar	Bar

Q: How prominent is the central bulge, compared with the rest of the galaxy?

Galaxies with a disk may also have a central bulge. Compared to the rest of the galaxy, for example any spiral arms, disk or bar, how prominent is the bulge? This is a bit of a tricky question, but just click the answer that you think best describes the bulge. Your answer can range from No bulge to Dominant, if the galaxy is mostly bulge with perhaps a barely visible disk or spiral arms. It's sometimes possible to be asked this question for an image where the whole galaxy appears like a bulge (in which case we call it an elliptical galaxy), for which the correct answer would be Dominant. However, for such objects you'll usually have answered 'Smooth' to the first question (as long as they don't have a bar, etc.) and so would not be asked this one.

Why not have a go… click on the galaxy images below to see our opinions.

Dominant	Just Noticeable	No Bulge	Dominant	Obvious
No Bulge	Obvious	Just Noticeable	Obvious	Just Noticeable
Obvious	Obvious	Dominant	Dominant	Just Noticeable

Q: Is there anything odd?

Until now we've asked you to concentrate on the galaxy itself. Now you can also look a little way around the galaxy. If there's a ring or a possible lens or arc in the image, if the galaxy is disturbed or irregular, or if there is something else odd, then click Yes here.

If you chose Yes, you'll be asked to specify the odd feature.

Q: Is the odd feature a ring, or is the galaxy disturbed or irregular?

You've told us there is something odd about this galaxy, or something nearby. What is it? Click on the answer which best matches the main odd feature. There might be a Ring feature in the galaxy, or there might be a feature due to gravitational lensing. These appear like arcs: curved sections of a circle centred on the galaxy, or sometimes multiple very similar looking small object arranged roughly symmetrically around the galaxy. They are very rare, but if you think you've spotted one, click Lens or arc. There are also three options to describe any odd appearance of the galaxy. A galaxy is Irregular if it is not smooth, but has irregular features which don't seem to form a spiral pattern. Disturbed galaxies resemble normal galaxies, with either smooth or spiral appearance, but which look like they have been distorted or twisted. Click Merger when the galaxy in the middle has another very nearby and there are signs that they are interacting: odd features or distortions in one or both galaxies. We'd also like to know if the galaxy has a dust lane running through it; look out for a thin dark streak across the bright parts of the galaxy.

Have a go at identifying the odd features in the images below… click on them to see what we think.

Merger	Disturbed	Dust lane	Ring	Irregular
Ring	Merger	Lens or arc	Lens or arc	Merger
Dust lane	Irregular	Disturbed	Ring	Dust lane

Galaxy Wars

After you have answered all the classification questions for a galaxy, you might be asked to compare it with another one.

If you have indicated that the galaxy you've been classifying has spiral arms, you'll be shown another galaxy and asked to click on the one which has the most prominent spiral arms. Choose the galaxy that has the most obvious and clearly visible spiral pattern. Sometimes it will be difficult to choose, don't agonise over it, just pick one. Other times the galaxy your comparing with might not even have spiral arms, then it's easy!

If you have told us that the galaxy you've been classifying has a bar, then you'll be asked to compare it with another galaxy. Click the image which shows the galaxy with the more prominent bar. As for the spiral comparison, don't over-analyse your decision, sometimes it will be tricky, often it will be easy.

See here to find out more about Galaxy Wars.

Zoo 2 Quick Links

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Astronomy Links

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• - Oxford University
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