Galaxy Zoo Talk

Could a Scientist please give a detailed explanation of the UKIDSS artifacts?

  • JeanTate by JeanTate

    The SDSS artifacts - at least the common ones - are well understood, and I think I can explain how they arise (well, to some level of detail anyway).

    However, quite a few of the UKIDSS artifacts have me stumped; I really have no idea how they arise! Could a SCIENTIST* familiar with how the UKIDSS telescope+camera+processing pipeline works please describe how at least the common artifacts arise? Thank you in advance.

    Here are some examples.

    enter image description here

    Why the grid-like pattern? Why an off-center ring? Why no diffraction spikes?

    enter image description here

    Green squares are very common, and they often may have the same (or similar) size and ratios of intensity (of the four corners); why? And why only green?

    enter image description here

    Small dark spots (1 pixel?), only in some images. Also a pair of green dots (less common than green squares).

    enter image description here

    Green ghost - why are green ones far more common than blue or red ones? And the bright blue star at the edge - really a double, or is it an artifact (it seems to have only one set of diffraction spikes)?

    My fellow zooites, please add more examples of different kinds of UKIDSS artifacts whose cause(s) you do not know (and are interested to learn)! 😄

    *ETA: by this I mean someone with the title 'SCIENTIST'

    Posted

  • zutopian by zutopian

    Here is my collection of UKIDSS artifacts.:

    http://talk.galaxyzoo.org/#/collections/CGZS000bld

    Posted

  • zutopian by zutopian

    Here is another discussion related to various UKIDSS artifacts.:

    http://talk.galaxyzoo.org/#/boards/BGZ0000003/discussions/DGZ0000fd1?page=1&comment_id=52a49f32134bb35d89000054

    Posted

  • KWillett by KWillett scientist, admin, translator

    Thanks for your questions and careful collections of these artifacts, @JeanTate and @zutopian. I've looked at some of the most common ones and just published a blog post about them.

    http://blog.galaxyzoo.org/2014/05/25/images-and-artifacts-in-galaxy-zoo-ukidss/

    Posted

  • KWillett by KWillett scientist, admin, translator

    Other artifacts I didn't discuss in detail:

    Odd/even images: (two-toned images cut in half) are the result of electronic cross-talk between the detector channels on the instrument. This usually occurs for stars that are bright, but not so bright that they saturate the image.

    Odd/even artifact

    Rings: For very bright stars, they emit enough photons to overwhelm the detector and saturate the image. In this case, the image is "flat-topped" in the center, and so the cross-talk effect manifests itself as a ring around the center source.

    Ring around the star

    Posted

  • zutopian by zutopian in response to KWillett's comment.

    In the blog post there is following statement.:

    We hope this has been useful, but please continue to discuss these in Talk and on the forums; particularly if there are any artifacts that impede your ability to make a good galaxy classification.

    The statement is somehow misleading in my opinion, because UKIDSS images are no longer displayed for classification, but it isn't mentioned in the blog post. It would have been better, if the blog post had been posted while the classification of the UKIDSS images was still continuing.

    Posted

  • KWillett by KWillett scientist, admin, translator

    That's true - my apologies for the somewhat awkward timing. Hopefully the explanation is still useful/interesting, even if belated.

    Posted

  • JeanTate by JeanTate in response to KWillett's comment.

    Yes it is, thank you.

    Do you happen to know why it took so long?

    As you've seen, many of the UKIDSS artifacts are very distinctive, and so zooites will often get excited when they come across them (as they do when they first see a green lightsabre satellite trail). I think being able to provide more than just a "it's an artifact" explanation helps maintain their interest, and is just the sort of thing zookeeperChris refers to in his Optimizing for interest : Why people aren’t machines blog post.

    Posted

  • zutopian by zutopian

    Thanks for the blog post about the UKIDSS artifacts. Well, it is "belated news", but it's nonetheless interesting/informative.
    Thanks also for the subsequent blog post about the completed classification of the UKIDSS images.:
    http://blog.galaxyzoo.org/2014/05/29/finished-with-galaxy-zoo-ukidss/

    Posted