AAS #14: Galaxy zoo finds people are screwed up, not the Universe

By Phil Plait | January 10, 2008 12:13 pm

A few months back, I blogged about GalaxyZoo, a very cool project that lets anyone classify galaxies from a professional astronomical survey of the sky. They got thousands of people helping, and have classified a million galaxies.


But they had a problem: people were finding significantly more counterclockwise-rotating spiral galaxies than clockwise. That’s a problem! We’d expect the numbers to be almost exactly the same. Did the GalaxyZoo folks stumble onto a new and previously undiscovered cosmological property?

Turns out, no. It’s not in the stars, it’s in ourselves. I interviewed astronomer Chris Lintott from GalaxyZoo, and he explains it all.

They have this on their blog as well.

By the way, here is an image to help you understand the CW versus CCW rotation problem:

Hope that helps. :-)

CATEGORIZED UNDER: Astronomy, Cool stuff, Science

Comments (33)

  1. Sergeant Zim

    Is it just me, or does the juxtaposition of the mirror images in the above post look vaguely pornographic?

    *Parediola/ID mode*
    Since the two images of the galaxy LOOKS like a pair of human breasts, it must be intelligently designed to be the image of Mary’s right mammary, which was used to suckle the baby Jesus

  2. Just Al

    I think it’s just you.


  3. ShavenYak

    Whew. Nice to know the Universe still makes sense.

    Wait a minute….

  4. Bad Albert

    Might help if they offered a free analog watch to every participant.

  5. tacitus

    What a beautifully simple way to solve the puzzle. I am assuming that they are presenting each image of the galaxies to multiple users and by showing the mirror image half the time, they should quickly be able to identify the problem galaxies — the ones people appear to be having the most difficulty with. These can them be singled out for more study and perhaps use as a test bed for getting more accurate results from the website. One could even grade the users according to their results and present the difficult images more frequently to the better users.

    Hmm… methinks Chris was only half-joking about the need for a psychology degree in helping with his work!

  6. Rav Winston

    Well, I think those pictures of the clockwise and anti-clockwise galaxies sitting next to each other look just like the opening sequence on Ultraman!

  7. bigjohn

    What I found was that with a lot of the images which appeared to be spiral it was very iffy to determine the direction of rotation. They were just too ill defined. In a few I thought I could just barely tell and selected accordingly. Most I simply clicked the “I dunno for sure” button. I probably used that selection most of all. As a result I felt kind of useless and, so, I only did about 810 galaxies total.

    A suggestion — have two galaxy analysis screens come up randomly, one with the anti on the right and one with the anti on the left.

  8. Michael H

    I am wondering if this has something to do with the fact that the written language (at least those of use using roman alphabet) is written from left to right. I am guessing the project has more participants from countries using the roman alphabet. The top edge of an anticlockwise galaxy points from left to right.

  9. RBH

    Chris Lintott remarked that he may have to become a psychologist. in fact, consulting someone with professional-level competence in designing stimuli for human perception studies might have been profitably consulted on the design of the interface, and on the ‘experiments’ they’re now attempting to do on the discrimination and classification of the irection of spirals.

    There was a time when astronomy was primarily a visual science and astronomers had a good handle on the varieties of artifacts generated by human viewers. With the now nearly total domination of observational astronomy by instrumentation, astronomers have lost that knowledge and would be well advised to consult with folks who have it.


  10. RBH

    And no bloody preview! Disregard the first “consulting” above, please.

  11. Bill Bones

    I’ve been wondering for a while wether the BA had screwed the images as thee looked reversed to my eyes, until I figured what could they mean by “clock-wise” and “counter-clockwise”: they are talking about how the arms spiral from OUTSIDE to INSIDE, whereas I was looking at how they spiral from INSIDE to OUTSIDE… and I was doing so because this is both how spirals are drawn and how natural spirals are grown: from inside to outside… ūüėČ I guess astronomers think, houm, different. Cultural conventions are powerful…

  12. William Astle

    It’s not the direction of the arms that is being referenced by “clockwise” or “counter-clockwise”. Rather is the direction of rotation. If a galaxy is rotating clockwise, the arms will radiate counter-clockwise. Remember, we’re not talking about drawing spirals but rather the direction of rotation of a spiral galaxy. So while astronomers think differently, this is simply a conflation of “the direction of rotation” and “the direction of spiral”.

    Unless I’m smoking dope and I’m completely wrong.

  13. Bill Nettles

    Bill & William, we’re all right! (good names, by the way)
    The spiraling appearance of the arms points opposite the actual direction of rotation because objects closer to the gravitational center have more angular velocity. The material at the outer edge lags behind creating a spiral appearance.

    The actual rotation is what the “center” does, not what the path of the arms looks like.

    And it’s really easy to mess up because our eyes are attracted to the arms and if we act “unconsciously” we’ll choose the direction they are “pointing.”

  14. JB of Brisbane

    Would it be appropriate to add that, on a smaller scale, the cloud bands in tropical cyclones (hurricanes, typhoons, etc.) work on the same principle, except that, due to the Coriolis (spell check) effect on low pressure systems, all northern hemisphere cyclones are anticlockwise, while all southern hemisphere cyclones are clockwise.

  15. This is a marvelously simple way of demonstrating the fallibility of human perception, and the ways that we can identify and overcome our weaknesses of perception by an application of reason. I definitely intend to use this as a case study in my next discussion of ascientific nonsense.

  16. John Fleming

    Maybe the late hour has numbed by humor center, but the ‘helpful’ display seems kind of needlessly demeaning and patronizing to the thousands of volunteers who selflessly and freely gave their own time to make this galaxy analysis work. For one thing, as previously stated, some images are simply too blurry to tell for sure, leaving it up to guesswork, in which case you can either try your best or just leave it undefined. Clockwise and counterclockwise rotation buttons on Galaxy Zoo are provided, complete with *graphical illustrations* thereof, so there’s no reason at all that even a beginner should mistakenly click the wrong one on a well-defined galaxy.

  17. IRONMANAustralia

    Hey Phil,

    Next time you are talking to Chris suggest he add a couple of new classification buttons, (just in case).

    [i]I don’t know if I can add images directly to this blog, (or even weblinks for that matter), but here goes …[/i]



  18. Maugrim

    John Fleming – yeah, I think you’re just tired. I doubt the BA intended to be insulting.

  19. JackC

    I have been classifying galaxies for some time now on GalaxyZoo – and I believe the issue Chris discusses is not only understandable, but should/may have been anticipated – and is even illustrated in this thread. The people classifying these objects are, on the whole, not expert and of differing “opinions” at to what constitutes ‘wiseness’ of the spiral galaxy. This happens despite the required pre-qualification one goes through to join the project.

    There is an interesting thing you can easily see though – if you find a particularly interesting – or even not so much – spiral, search for it in the forums and see what you find. To date, I have found both flipped and rotated versions seen by others.

    It is immediately apparent that GZ does an outstanding job of anticipating human bias and attempt to minimise it by presenting alternate views to many, many people. I am even certain (though I don’t bother to record it) that I see the same presentation over and over, in different rotations, as kind of a “cross-check” of my own work.

    As to those galaxies that are “too difficult to determine” – they provide a “Don’t Know”, as well as an “Edge-on” button that they explicitly state in the FAQ to use in such cases.

    I wish that I could run sort of a “sanity check” on my own work and see what would amount to maybe a qualified rating on the galaxy images to see how well I have done. It is kind of like taking a test, but never knowing what your score was. Sure, you could take the pre-qual test over again, but that isn’t the same thing.


  20. SF Reader

    Alas, I know far too many people (starting on college 30 years ago!) who’ve never had an analog watch and don’t even get the “clock” reference.

    Of course, there are all the people who are rather unclear on left and right…

  21. N'Dalia


    it really doesn’t matter if you’re familiar with analogue watches or not to understand how to classify:

    there are icons at the spiral galaxy buttons, which even the dumbest classifiers could compare to the galaxy image quite easily…

    if your brain doesn’t work, use your eyes & common sense

    or how they say in germany:
    glotzen off, arschkrampe! ūüėČ

  22. TheUnknownFactor

    Most of the images are so horrid on that website one can’t determine the rotation. Showing two high resolution images as if the problem was so simple is laughable. Most of them look like blobs of pixels anyways.

  23. Strange – I seem to be seeing more clockwise galaxies and I DO know which are which. =)

    Or maybe I should identify more samples before making statements like that…

    By the way – classifying galaxies is fun. I finally know how to pass some time while making myself useful when I have nothing better to do. ūüėÄ

  24. Hmmph! Seems everyone missed the obvious.
    Look at a clock face – the hands move clockwise. (Figuratively) Look at the clock’s backside and the hands move counterclockwise.
    All galaxies rotate clockwise – just look at them from the “top” (face) side!

  25. john

    Nice! Thanks for update.
    But what I really want to know is why did they call it GalaxyZoo instead of ZwickyPedia?

  26. Robert Carnegie

    Thanks for the suggestion about breasts. I now inevitably see this web page as Chris Lintott somehow holding up a very large pair of galactic breasts. We should, of course, remember where the word “galaxy” comes from. At least according to Wikipedia. http://en.wikipedia.org/wiki/Galaxy It is from Hera’s happybags. (Clockwiseness not specified.)

    Since the suggestion of flipping pictures has already been made… how about trying other angles too?

  27. Hugo

    Ah, there’s no news like old news.

    Improbable.com has a nod towards this post…albeit it’s six months late.

    See here: http://improbable.com/2008/07/15/in-the-stars-in-their-heads/

  28. Willem Vogel

    Isn’t it so that if you could observe a clockwise galaxy from the backside it is rotating counter clockwise? Looking on a transparant watch from the backside makes it seem rotating counter clockwise. So every galaxy rotates both clockwise and anti clockwise at the same time and the direction of rotation of a galaxy depends on the position of the observer and not the galaxy! All we have to do now is find a different position…


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


See More

Collapse bottom bar