Galaxy Zoo Talk

Why are there so many artifacts?

  • Qexilber by Qexilber

    Galaxy Zoo says it would every now and then show stars of artifacts that aren't galaxies. Why do I stumble in so many of them? Did I do something wrong classifying something like that as an artifact?


  • Rick_N. by Rick_N. in response to Qexilber's comment.

    I am not a member of the GZ team, but perhaps I could give some opinions? Firstly, what are you expecting? Secondly, the images are mainly from a robotic telescope on the ground, so might not be 'Hubble' type images. Thirdly, part of the process of GZ is to separate the good images from the bad images. This saves the scientists using the data a huge amount of time and effort. Fourthly, GZ is about cassifying galaxies as ellipticals, spirals etc.; not necessarily looking for beautiful objects. Fifthly, stars in our galaxy are always going to be over-exposed, as the SDSS telescope is set-up to look for very distant and thus faint objects. Filtering problems are part of that.

    I'm sure there are other reasons, but I hope these opinions help.


  • Budgieye by Budgieye moderator

    We are working at the frontiers of knowledge, and with some practice, we amateurs can learn to recognize errors and artifacts in the images. Believe it or not, the images have already been extensively cleaned and sorted by computer software, There are several million "close" galaxies to look at, and a billion stars. SDSS uses a computer program to sort out the stars and the galaxies, so we don't have to look at all billion stars. Stars are "round" and galaxies are "extended sources" ie elliptical or fuzzy. The software makes errors eg.

    several close stars = extended source = galaxy

    star taken under poor seeing conditions = fuzzy = galaxy

    There are other errors too. But I agree that it would be nice to block off some of the more obvious errors so that we see them 10 times, then we don't see them any more. But we have to be careful, because we might be blocking off distant quasars or unusual stars and galaxies. So, this is where Galaxy Zoo uses people to help the computer.