If you took part in Galaxy Zoo 2, then you'll find much that is the same as before. To skip to the new part of the tutorial click here
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.
Smooth |
Features or disk |
Star or artifact |
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 Features or disk:. 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.
Smooth
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Features or disk
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Star or artifact
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Features or disk
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Features or disk
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Features or disk
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Features or disk
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Smooth
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Star or artifact
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Smooth
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Completely round |
In between |
Cigar shaped |
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
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In between
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In between
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Cigar shaped
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Completely round
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In between
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Cigar shaped
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Completely round
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Cigar shaped
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Completely round
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In between
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Completely round
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Completely round
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Cigar shaped
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Cigar shaped
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Yes |
No |
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
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Yes
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No
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No
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Yes
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No
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Yes
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No
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No
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Yes
|
Rounded |
Boxy |
No bulge |
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
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Rounded
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Rounded
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No Bulge
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No Bulge
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Rounded
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Boxy
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No Bulge
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Rounded
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Boxy
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Spiral |
No spiral |
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
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No Spiral
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No Spiral
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No Spiral
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Spiral
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Spiral
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Spiral
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Spiral
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No Spiral
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No Spiral
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Tight |
Medium |
Loose |
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
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Loose
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Tight
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Tight
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Loose
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Medium
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Loose
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Tight
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Tight
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Medium
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Medium
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Medium
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Tight
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Medium
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Loose
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1 |
2 |
3 |
4 |
More than 4 |
Can't tell |
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.
Why not have a go and see if you count the same number as us! Just click on the galaxy images below.
Can't tell
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More than 4
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1
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1
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More than 4
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2
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Can't tell
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2
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4
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2
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3
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Can't tell
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More than 4
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1
|
4
|
Bar |
No bar |
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
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No Bar
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Bar
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No Bar
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Bar
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Bar
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No Bar
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Bar
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No Bar
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Bar
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No bulge |
Just noticeable |
Obvious |
Dominant |
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
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Just Noticeable
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No Bulge
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Dominant
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Obvious
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No Bulge
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Obvious
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Just Noticeable
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Obvious
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Just Noticeable
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Obvious
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Obvious
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Dominant
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Dominant
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Just Noticeable
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Yes |
No |
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 choose Yes, you'll be asked to specify the odd feature.
Ring |
Lens or arc |
Disturbed |
Irregular |
Other |
Merger |
Dust lane |
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
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Disturbed
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Dust lane
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Ring
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Irregular
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Ring
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Merger
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Lens or arc
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Lens or arc
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Merger
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Dust lane
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Irregular
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Disturbed
|
Ring
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Dust lane
|
Yes |
No |
If you took part in earlier versions of Galaxy Zoo, you'll probably notice that Galaxy Zoo: Hubble contains a lot of messy objects that don't fit neatly into the usual flow of questions. That's because many of the galaxies featured in Galaxy Zoo: Hubble are seen at an early stage of their development, when the universe was relatively young. These objects haven't yet developed the regular spiral or elliptical appearance common today, but instead often have a clumpy appearance, comprising several blobs or irregular shapes that seem to be associated with one another. We've added some new questions to deal with these. First of all we need to know if the galaxy you are looking at has a clumpy appearance. Only click Yes if the appearance of the galaxy is dominated by distinct 'blobs' of light. If the galaxy simply has a smooth irregular appearance, there are clear spiral arms, or it appears to be an edge-on disk, then click No.
Why not have a go and see if you can spot clumpy galaxies! Just click on the galaxy images below.
No
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No
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No
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No
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No
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Yes
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Yes
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Yes
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Yes
|
Yes
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2 |
3 |
4 |
More than 4 |
Can't tell |
1 |
If you've identified a clumpy galaxy, the first thing we need to check is how many clumps you can see. Sometimes it will be easy to answer this question, other times it won't be so clear, but just choose the number of clumps that seem to make up the galaxy. We'll ask you a few more specific questions if there is more than one clump.
Click on the images below to see how many clumps we counted for these galaxies.
1
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2
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3
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4
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More than 4
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Straight Line |
Chain |
Cluster |
Spiral |
How are the clumps arranged? Sometimes they will be in a straight line, or they might appear to be lined up but in a curving or wiggly manner like a chain. In other objects they might not be lined up at all, but just be grouped together in a cluster. Finally, you might be able to see that the clumps form a spiral pattern, like a lumpy spiral galaxy.
Click the images below to test that you can recognise the different arrangements.
Chain
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Chain
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Chain
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Cluster
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Cluster
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Cluster
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Line
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Line
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Spiral
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Spiral
|
Yes |
No |
Sometimes one of the clumps will be obviously brighter than all the others. If that's the case, then answer Yes to this question.
Click on the images below to make sure you can spot which galaxies have an obvious brightest clump.
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No
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No
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Yes
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Yes
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Yes
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Yes |
No |
If there is one clump that is brighter than the others, then we want to know if that clump appears roughly in the centre of the galaxy or not.
Check you can identify galaxies which have a central brightest clump by clicking the images below.
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No
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No
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No
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Yes
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Yes
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Yes |
No |
Even though the galaxy is clumpy, it might appear fairly regular and symmetrical, or then again it might not. Let us know which by answering this question.
See if you agree with us by clicking the images below.
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No
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No
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No
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Yes
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Yes
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Yes |
No |
Do the clumps seem to be just parts of a bigger galaxy, or are the clumps all that you can see?
See if you can tell the difference by clicking the images below.
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No
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No
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Yes
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Yes
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Yes
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Thanks for all your efforts in identifying possible gravitational lenses — with the new release of the Zoo, we have an even harder challenge for you. The galaxies that you will be looking at come from a region observed by the Hubble Space Telescope called the Extended Groth Strip (EGS). Galaxies from this area have already been searched for gravitational lensing through visual inspection Moustakas et al., 2007 and by an automated robot Marshall et al., 2009 the simulated ones were used to teach the robot what lenses look like. However, it could well be that both of these methods may have missed lenses, so our challenge to you is to beat the astronomers and the robot to see if you can find new undiscovered lenses.
To help you along the way Phil has made a couple of movies of objects you are likely to see in your galaxy classifications:
You can also download galleries of the lenses and non-lenses.
For those of you who haven't seen it already, there's a nice guide to lensing for the SDSS Zoo made by Budgieye: Zooite Guide to Strong Gravitational Lenses.
Happy hunting!
Aprajita & Phil
Well done for reading the tutorial. Click here to start classifying!
