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Frequently asked questions

Click on the questions to see the answers – or ask your own.

Competition closed! The competition to win a wi-fi telescope, or an iPad for your school, has now closed. However, we’d love you to continue classifying galaxies!


Do I need to register to do Galaxy Explorer?

No, you don’t need to register to start classifying the galaxies.

However, there are good reasons to register – it means you can track the number of galaxies you’ve done; and save your favourite galaxy images to a photo gallery.

>Start classifying

Can people from outside Australia participate?

Absolutely. Astronomy is an international subject and we’d love anyone on the planet to join in.


How do I change my password?

You can change your password via the ‘login’ button on the top right of the Galaxy Explorer website. Click on the ‘Forgotten your password’ link.

You can then go through the process to ‘recover your password’ which will allow you to set a new one.


How do I get involved?

Before you start you’ll need to do a quick tutorial that explains how to classify galaxies. This should only take a few minutes. Then you’re ready to get galaxy gazing.

>Start classifying

How will I find out the results of our work?

You can stay in touch with any outcomes from Galaxy Explorer by
FacebookABC Science and National Science Week
TwitterNational Science Week and ABC Science
Email –  ABC Science Updates

Can children do Galaxy Explorer?

Yes, children of (roughly) eight and older can competently classify the galaxies, and will probably get a massive buzz from doing it. 

Children do need parental approval to register. Parents and teachers should ensure that children have watched the tutorial and understand what they’re supposed to do.

>How do I get my school group involved?

Why do I need to watch a tutorial before I start classifying the galaxies? 

Classifying the galaxies is an important job and we need you to do the best job you can.  The tutorial will give you a basic understanding of how to classify the galaxies and also show you how to use the classifying interface.

Remember, Galaxy Explorer is a citizen science project and the work you do will contribute to a real scientific project.

How do I watch the tutorial again? 

You can watch it again at any time – click on ‘Help’ from the classifying interface and you’ll find the link to ‘Tutorial’ in the list.

Is there more help available? 

Take a look through the Guide to classifying galaxies – this is a photo gallery of classified galaxies that will give you a bit of extra insight.

The FAQ also has a lot of information in it.

Classifying the galaxies can be tricky – some will be obvious and you’ll breeze through them. Others are hard and even the astronomers disagree on what’s in the images! Just try and do the best you can. If you have a particular question you can send it to us and we’ll endeavour to answer it.

Can I get some feedback on how I’m going?

It would be lovely to be able to give feedback, but one of the main purposes of Galaxy Explorer is to lessen the work for the scientists. And asking them to review people’s performance would massively increase it!

Don’t forget, the system is set up in such a way that each image is processed by at least 5 citizen scientists. The astronomers will then look more closely at the images that received a range of different classifications – making the assumption that they were difficult to classify – and will check them over themselves.

What do I do if I make a mistake?

You can start classifying a galaxy again by clicking on the ‘Restart’ button at the bottom left of the classifying window.  However, once you’ve clicked ‘Finish’ for an image then you can’t go back and re-do it.

Don’t worry too much if you think you’ve made a mistake – each image will be done by five different people – it’s a process designed to weed out any little errors.



How do I get my school involved?

Take a read through our suggestions on getting your students involved with Galaxy Explorer.

>How do I get my school group involved?

>Information on the schools competition.

I didn’t realise I had to give my password to the students – how do I change it?

You can change your password via the ‘login’ button on the top right of the Galaxy Explorer website. Click on the ‘Forgotten your password’ link.

You can then go through the process to ‘recover your password’ which will allow you to set a new one.


Classifying galaxies

How do I classify galaxies?

 The galaxies are classified based on their shape and appearance, including their colour and any features they have (such as spiral arms, bulges or bars).

To classify the galaxies you’ll be lead through a series of simple questions about its appearance.

You’ll need to watch a short tutorial before you begin.

Remember, classifying the galaxies can be tricky even for the astronomers sometimes. Just do the best you can.

I can see more than one galaxy – which one do I classify?

Sometimes it can be tricky to work out which galaxy to classify, but there are two lines pointing to the very centre of the image and the galaxy you need to classify will be there.

Even if there is a bigger galaxy to the side, it’s the one in the very centre that you need to classify.

If you realise at this point that you’ve been analysing the wrong thing, you can click ‘Restart’ to go back and change your answers.

The image is distorted and I can’t classify the galaxy – what do I do? 

Occasionally this will happen. If for any reason at all you can’t classify the galaxy you can click the ‘Can’t classify’ link at the bottom right of the classifying interface.

Some of the reasons you may not be able to classify an image is if there is a strange colour palette; you can’t make out a galaxy at all; you’ve got absolutely no idea what to do!

I’m having trouble working out if my galaxy has features.

It can be hard to make out if a galaxy has features or not. Sometimes the features can be very subtle – just the hint of a bar, bulge or spiral arm is enough to classify it as having features.

There are examples of bulges, bars and spiral arms in ‘The guide to classifying galaxies’ – looking through these should make you feel a bit more confident. Basically, if you think there are features there – then classify it as having features.

And don’t forget, each image will be classified by at least five people so you’re not the only one classifying that galaxy.

There’s a big bright thing in my image – what is that?

If it’s not in the centre of the image then it could be a star, another galaxy or an image distortion caused by the telescope.

A galaxy will be roundish/oval/cigar-shaped or irregular in shape. It might be blue/white/yellow/orange.

A star will be round and could be very bright. It might be green/blue or orange.

Image distortion looks like a sun-burst pattern or strange lines. What you’re seeing is distortion caused by the telescope. Just ignore it.

I’ve found something weird. What should I do?

If you can’t classify the galaxy at all then click on the ‘Can’t classify’ link.

However, if it’s something weird then you might want to share it on Facebook or Twitter (with the hashtag #GalaxyExplorer)

I’m not sure if my cigar-shaped galaxy has a bulge?

This is a tricky one! Look for a bulge around the middle of the galaxy, it might look like a pregnant tummy. Or there could just be a brighter glow at the centre of the galaxy.

If in doubt, just classify the galaxy as a cigar-shaped galaxy.

Where do the photos come from?

The images in Galaxy Explorer come from two telescopes: SDSS 2.5m telescope at the Apache Point observatory, New Mexico provides the optical component that goes into the images; and the infrared component comes from the VISTA telescope in Chile.  The images were put together as part of the GAMA survey.

Read more on the science behind Galaxy Explorer.

The galaxy has blue/green and red pixels. How should I classify it?

This sounds like a tricky galaxy, but because it has blue/green you should classify it as a blue/green galaxy.

Go with the dominant colour when classifying the galaxies.

Outside the target is a barred spiral galaxy, is this of significance?

It’s nice to see spiral galaxies nearby, but the galaxy you need to classify is the one right in the centre. That other galaxy will be at the centre of its own image, and will get classified then.

I’ve got a red coloured galaxy. Do I select the yellow-orange option?

Yes, if you have a red coloured galaxy please select the yellow-orange option.

Luke Davies, astronomer says…
“We have found that the colour scaling that we use in the galaxy explorer tool that most of the galaxies either look blue-green, or yellow-orange. The red galaxy you can see just falls at the extreme end of the yellow-orange classification. For the purposes of how we separate out the galaxies based on your classifications, we would definitely want this system to be defined as ‘yellow-orange’.”

Fitting the ring

How tight should the ring be? 

The purpose of the ring is so astronomers can calculate all the light emitted by the galaxy. So it needs to encompass the galaxy, and fit reasonably snugly. However, it’s okay to have a bit of space around the galaxy.

Take a look at the Guide to classifying galaxies for some examples of fitted rings.

What if the ring goes around two galaxies? Do I fix that up?

Yes, the ring should only go around the galaxy you’ve been classifying.

How many stars should I mark?

Mark as many bright stars as you can see inside the red and green rings.

How do I know if it’s a star or not?

The best way to work out if it’s a star or another galaxy is by shape – stars will be round. They may be quite bright too, but not necessarily. They might be tiny or large.

Should I mark other galaxies?

No, don’t mark other galaxies.

There’s a really big star but it’s outside the red ring – should I mark it?

You only need to mark stars inside the red or green rings. However, it won’t matter if you mark one outside the ring – it just won’t be used by the astronomers.

Should the red dot be at the centre of the galaxy or at the brightest spot in the galaxy?

The red dot should go at the centre of the galaxy, which is often, but not necessarily the brightest spot.

Help! I can’t fit the ring or mark stars!

A few people have reported issues with fitting the ring or marking the stars. If you’re having difficulty with this part of Galaxy Explorer, then just do whatever you can.

Don’t forget, each image will be done by at least 5 people so someone else will have managed to point out the stars and fit the ring (we hope!)

I’m using an iPad and having trouble fitting the ring and marking the stars.

It is a little tricky using the iPad to fit the ring and click on the stars.

The blue ring that’s appearing when you tap is for marking stars. You can make the ring disappear by tapping on it again.

Try holding your finger onto the green ring, rather than tapping it, to drag it.

The science

Why do scientists want us to classify these galaxies?

The images used in Galaxy Explorer are part of a big project looking at the history of the universe and trying to understand how galaxies evolve.

It’s what we call ‘blue-sky’ science – there’s no reason to do this research other than for the sake of knowledge itself. And sometimes out of this knowledge new technologies may eventuate.

You can read more about the science behind Galaxy Explorer in – Why classify far away galaxies?

The reason we’re asking citizens to help is that there are just so many images to be processed. Unfortunately it’s not a job that a computer could do – but if lots of people help out then the load is shared.

What are scientists hoping to find?

The scientists want to create a census of galaxies of different ages. They can then use this information to create a model of galaxy evolution throughout the history of the universe. This knowledge may also help answer some of the inconsistencies we see between Einstein’s equations of how the universe should behave, and what we actually see occurring. These inconsistencies have led to the concepts of dark energy and dark matter. So this research may help shed some light on how the universe works.

What does the colour of a galaxy tell us?

Luke Davies, astronomer says…
“The colour mostly tells us the age of the stars in the galaxy, or part of the galaxy if it has different colour regions.

“Young stars are generally hottest and produce higher energy/shorter wavelength light – this light is blue.

“Older stars are cooler and produce more light at red wavelength.

“Our sun is yellow/white because it sits somewhere in-between these two ranges, it is about average age, not too blue and not too red.

“So a blue galaxy contains younger stars than a red (yellow-orange) galaxy.

“If you want to learn more about light of different wavelengths check out this great interactive website and video describing light.”

How was the distance of a galaxy from earth calculated?

Luke Davies, astronomer says…

“The distance is calculated using redshift. This is not measured from the images you see, but from a spectrum of the light from the galaxy. A spectrum is essentially the amount of light we measure as a function of wavelength. The spectra for these galaxies were taken using the Anglo-Australian Telescope in NSW and form part of the Galaxy and Mass Assembly Survey.

“In these spectra we see characteristic bright lines which are produced from atomic transitions in the elements which make up the galaxy. For example, we see bright lines corresponding to atomic transitions in Oxygen, Hydrogen and Nitrogen. From our experience here on earth, we know exactly the wavelength at which these lines should appear. However, when we look at distant galaxies, the lines are always ’shifted’ to redder wavelengths, this is a redshift. We also find that this shift is proportional to the distance to a galaxy (when it is measured in other ways). This the famous result Edwin Hubble found in 1929. So using the redshift, and knowing the relationship between redshift and distance, we can use it to work out how far away a galaxy is.

“What’s going on? Well the redshift is produced by the expansion of the Universe. As light has a finite speed limit, the further away a galaxy is away from us, the longer the light from it has travelled though space. In that time the Universe has expanded, and this is what causes the redshift. So…. using what we know about the expansion of the Universe (called out cosmological model) we can relate the redshift to both a distance to the galaxy and the time that the light has been traveling through space to reach us.”

Do the images show “red shift” ? In what way?

Luke Davies, astronomer says…
“The images will subtly show a redshift, in that the light will be ever-so slightly redder for more distant galaxies, but not at a level that we can see in these images. We use the galaxy spectra to calculate the redshift.”

Some images that include galaxies approximately 4 billion light years away are surrounded by “empty” blackness. Does this indicate a “limit” to the observable universe?

Luke Davies, astronomer says…
“This occurs because the observations used in the Galaxy Explorer are not sensitive enough to see galaxies that are either further away or are less massive than the ones we see.

“The universe is crammed full of galaxies, but any image that we take is limited to only detect galaxies above a certain brightness.

“Galaxies that are fainter than this can’t be seen. These galaxies can be fainter either because they are further away, or because they contain less stars.

“The images used in the Galaxy Explorer come from the Sloan Digital Sky Survey (SDSS), which is amazing in the area of the sky it observes. Things like the Hubble Space Telescope, observe very small areas of sky but see galaxies which are much, much fainter and therefore much further away (such as in the Hubble Ultra-Deep Field). But even with Hubble, we still haven’t reached the edge of the observable universe!”

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