# 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

• 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 Jul 30 '16 at 6:29
• @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 – RononDex Jul 30 '16 at 11:32
• 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. – James K Jul 30 '16 at 21:09
• 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 – James K Jul 30 '16 at 21:12
• The word you are looking for is "meteor", and I hardly think that's what it looks like on the picture. – nataliaeire Aug 30 '16 at 14:50

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.
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.
• @RononDex looks like 2230 $e^-$ is the maximum value at ISO 1600 so indeed it could be a minimum ionizing particle! Thanks! – uhoh Aug 31 '16 at 12:17