Could this be a cosmic ray hit on my cameras sensor (CMOS, DSLR)?

  • While taking pictures of the bubble nebula I noticed a very strange artifact on only one of my pictures. It can't be a satellite since its not a straight line and this is a 90s exposure that should make a line much longer. Also I doubt this is just readout noise from the camera (image is unstretched, unedited) since hot pixels don't form lines. So could this be a cosmic ray hit? If not does anyone have an idea what this could be?



    The image was taken with my Canon 7D Mark II @ISO1600, 90s exposure.
    Celestron C8 SGT (XLT), Celestron Advanced VX



    enter image description here



    enter image description here


    Could it be something closer to earth like dust/speck of dirt/pollen/bug eyeball/sap/water droplet/etc that was on the lens and shifted during the exposure?

    @iMerchant I highly doubt that, since it looks like something that was smaller than 1 pixel and still extremly sharp (compare it to the stars in the background). From this I concluded it must be something on the sensor of the camera, not something that came through the optics

    I'll let others give definitive answer to this, but cosmic rays can leave tracks on ccd. The fact it is not straight suggests a rather loe energy electron, rather than a high speed muon or similar.

    Since it is very narrow, i think it must be something inside the camera, as an thing outdide would be blurred by imperfection of the lens. Some kind of stray elecron seems most likely

    @RononDex: You could test the hypothesis that it's a cosmic, if you manage to repeat the same observation in the same field with the same parameters as given.

    @AtmosphericPrisonEscape Aren't cosmic ray hits kind of random? If so how would a repeat of the same show its validity?

    @RononDex: If it's not there the second time, it was a cosmic. That's at least the usual assumption. Of course it could be also any other kind of non-repeatable event on your lens, but cosmics are the most frequent.

    To me it looks like an airplane taking a curve (red-green-red).

    @ott-- it seems unlikely that it has been something that I saw through the telescope, because it is completly sharp and not washed out like the stars in the background.

    Possibly a grain of dust burning up as it entered the atmosphere.

    The word you are looking for is "meteor", and I hardly think that's what it looks like on the picture.

  • uhoh

    uhoh Correct answer

    6 years ago

    It's a track about 50 pixels long, at 4.1 $\mu m$ per pixel that's 200 $\mu m$ in the plane of the sensor.



    It's about 1 pixel wide, quite lumpy, and seems to change direction a bit. It really fits the description of an ionizing particle. There are multiple possible sources,



    I'm pretty sure @JamesK has nailed it as an electron, but what else can we learn? There must be some way to get a very rough idea of how many $e^- h^+$ pairs correspond to a fully exposed pixel at "@ISO1600", then we could convert it to a dE/dx and see if it's minimum ionizing or if it's much higher.



    Going diagonally, with a density of 2.3 g/cm${}^3$ that's about 1.3 mg/cm${}^2$ areal density per pixel. A [minimum ionizing particle] at 1.5 MeV / g cm${}^2$ would deposit only about 2000 eV which would make less than 1000 $e^- h^+$ pairs. That might correspond to a bright pixel. It's not out of the question that it's a minimum ionizing particle.


    That's a very interesting read. If it might help you for further analysis, this is a page that analysis the sensor of my camera really deeply (with all the different read noise, gain, etc for each iso setting): http://www.clarkvision.com/reviews/evaluation-canon-7dii/ Alternatively this is another page with some more info: http://www.sensorgen.info/CanonEOS-7D-Mark-II.html **Note that this image was taken while the sensor was at a temperature of around 34°C**

    @RononDex looks like 2230 $e^-$ is the maximum value at ISO 1600 so indeed it could be a minimum ionizing particle! Thanks!

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