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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

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  • $\begingroup$ 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? $\endgroup$
    – iMerchant
    Commented Jul 30, 2016 at 6:29
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    $\begingroup$ @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 $\endgroup$
    – RononDex
    Commented Jul 30, 2016 at 11:32
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    $\begingroup$ 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. $\endgroup$
    – James K
    Commented Jul 30, 2016 at 21:09
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    $\begingroup$ 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 $\endgroup$
    – James K
    Commented Jul 30, 2016 at 21:12
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    $\begingroup$ The word you are looking for is "meteor", and I hardly think that's what it looks like on the picture. $\endgroup$ Commented Aug 30, 2016 at 14:50

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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.

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    $\begingroup$ 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): clarkvision.com/reviews/evaluation-canon-7dii Alternatively this is another page with some more info: sensorgen.info/CanonEOS-7D-Mark-II.html Note that this image was taken while the sensor was at a temperature of around 34°C $\endgroup$
    – RononDex
    Commented Aug 31, 2016 at 10:50
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    $\begingroup$ @RononDex looks like 2230 $e^-$ is the maximum value at ISO 1600 so indeed it could be a minimum ionizing particle! Thanks! $\endgroup$
    – uhoh
    Commented Aug 31, 2016 at 12:17

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