What causes the "green threads"?

As in here:

And here:

And here:

ETA: I seem to have forgotten how to make an image URL display as an image :frowning:
ETA2: I edited the above, using the HTML “img” tag, per dstn’s suggestion.

1 Like

Ahh, these are cosmic rays. They’re bright green here because they only appear in one of the images (in this case one of the “r”-band images that becomes green in these renderings). Cosmic rays are particles (often from radioactive decay) that hit our detectors, but don’t come through the optical elements.

If you click on the “Single Image Cutouts” link, you’ll see that it only appears in one of the images. Also, if you look around, you should be able to see ones that are red and blue as well. They’re often a little harder to see; the green ones really stand out!

Finding and ignoring these cosmic rays is something we’re hoping to improve in our upcoming DR8 release.


1 Like

Thanks! :slight_smile:

I did find some red ones (see below), but haven’t yet noticed any blue ones (I’m sure they exist).

Am still stumped re how to display the image rather than just the URL …

PS At least the atmosphere greatly reduces the numbers of cosmic rays (CRs) … if one looks at raw Hubble images, the number of CRs can be huge. Even when there are two overlapping images, with good “rejection” software/routines, some CRs still get through.

ETA: edited to show image, using HTML “img” tag.

(to upload an image: in the “compose” dialog box, does it work to click the ‘image’ icon (whose tool-tip text says “Upload”), and then it gives you an option to upload an image, or give a URL?)

Test: using the image icon, and copy/pasting the URL:


I did try that before, and got the same result …


Sorry for posting a suggestion without trying it myself first!! The first link above is what I get when I do what I suggested – no image – and the second is where I appending a fake “&suffix.png” to the URL, which I guess makes it end in “.png” and makes this forum software believe it might be an image…?

I’ll see if I can find anything in the settings to fix that behavior.

Best wishes,

PS – you can also write it as an HTML “img” tag –

    <img src="  --the URL-- ">


<img src="http://legacysurvey.org//viewer/jpeg-cutout?ra=121.7441&dec=6.4145&zoom=16&layer=decals-dr7">


That is very cool, thank you so much! :smiley:

I like the HTML “img” tag, and am kicking myself a little bit for not thinking of it myself …

Okay, so I couldn’t find any relevant setting in the forum software, but what I did was change the viewer web site so that when you click on the map, the popup link to the cutout contains “cutout.jpg?ra=…”, and that seems to be enough to hint to the forum software that it’s a jpeg.

Thanks for pointing this out :slight_smile:


Ignore the green squiggle - what about that weird “halo” on the third image?

Yes, that’s amazing – like an extra ring on that galaxy!

I even started a separate thread on this galaxy: What kind of galaxy do you think this is?

Any takers?

I found some blue threads!

1 Like