Green and Blue Dots
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by BenoitBoulet
i noticed there are green and blue (hollow) dots on the right side of this image. I'm really not sure what i'm looking at here, as it could be a digital artifact. However they do look strange.
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by Capella05 moderator
Both of those dots are optical artifacts, so they are not real.
I am more concerned that your image is incorrectly sized! #wrong_size
Happy Hunting!
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by sat666leg
i've seen a few of these and when i switched from decals image to models there was a pair of purple edge on galaxies way back in the image..?
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by Capella05 moderator
The rings are caused by dust on the either the filter or the window of the CDD camera. The dust causes a shadow on the detector.
Do you have an example of the purple edge on galaxies you saw?
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by sat666leg
il check
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by klmasters scientist, admin
That size is really way off. Lots going on there, so it looks like the automated pipeline indicating the size of the central galaxy is really wrong.
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by sat666leg
note on size i've had about 3/4 like that..
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by Capella05 moderator
Here is a sceenshot of the purple ring artifact in the DECaLS image explorer:
and the image when switching to the DECaLS model examiner:
It looks like the algorithms that are used to generated the model did not know how to interpret the artifact, so it assumed it was a pair of purple non-existent galaxies. I am sure @KWillett will be able to give more information on why the model did this.
It would also be interesting to see how other artifacts get modelled!
Hope this helps, and thanks for pointing it out 😃
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by sat666leg
look at the initial image right at the top on the left ..in decals model the dots are solid green and blue
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by Capella05 moderator
Can you give the RA / DEC? so I can have a closer look?
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by sat666leg
there in the image above that started this discussion..
or right here to the left..
RA, DEC= 318.3438, 0.9837.Posted
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by dstn
These blue and green things are an asteroid. In these images, blue = g band, green = r band, and we take those images back to back. The asteroid moves that much in the time between exposures (though shouldn't they be streaked then?). They are "hollow" because of over-aggressive masking of pixels around saturated pixels. When given 'hollow' objects, the source detector can find multiple objects which then get fit as the closest thing it can find, such as these extended and strangely colored "galaxies".
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by KWillett scientist, admin, translator
Great to know - thanks, @dstn.
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by ElisabethB moderator
You learn something new everyday ! 😄 I would have gone with artefact in a heartbeat !
Thanks !
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