<p>It's a track about 50 pixels long, at <a href="https://photographylife.com/reviews/canon-7d-mark-ii" rel="noreferrer">4.1 $\mu m$ per pixel</a> that's 200 $\mu m$ in the plane of the sensor. </p>

<p>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, </p>

<p>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 <em>very rough</em> 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.</p>

<p>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.</p>

CC BY-SA 3.0
2016-08-31T10:50:59.297Z
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
CC BY-SA 3.0
2016-08-31T12:17:00.973Z
@RononDex looks like 2230 $e^-$ is the maximum value at ISO 1600 so indeed it could be a minimum ionizing particle! Thanks!
uhoh
CC BY-SA 3.0
2016-08-30T16:31:19.357Z
2016-08-30T16:31:19.357Z
uhoh
<p>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?</p>

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

<p><a href="https://i.sstatic.net/BNcJH.jpg" rel="noreferrer"><img src="https://i.sstatic.net/BNcJH.jpg" alt="enter image description here"></a></p>

<p><a href="https://i.sstatic.net/IQMfI.png" rel="noreferrer"><img src="https://i.sstatic.net/IQMfI.png" alt="enter image description here"></a></p>

CC BY-SA 3.0
2016-07-30T06:29:22.937Z
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
CC BY-SA 3.0
2016-07-30T11:32:12.800Z
@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
CC BY-SA 3.0
2016-07-30T21:09:14.610Z
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
CC BY-SA 3.0
2016-07-30T21:12:08.040Z
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
CC BY-SA 3.0
2016-07-30T22:13:43.750Z
@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
CC BY-SA 3.0
2016-07-31T08:17:53.633Z
@AtmosphericPrisonEscape Aren't cosmic ray hits kind of random? If so how would a repeat of the same show its validity?
RononDex
CC BY-SA 3.0
2016-07-31T10:53:42.800Z
@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.
AtmosphericPrisonEscape
CC BY-SA 3.0
2016-08-01T19:53:57.977Z
To me it looks like an airplane taking a curve (red-green-red).
ott--
CC BY-SA 3.0
2016-08-02T10:39:07.287Z
@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.
RononDex
CC BY-SA 3.0
2016-08-30T13:37:21.987Z
Possibly a grain of dust burning up as it entered the atmosphere.
Off Grid Bob
CC BY-SA 3.0
2016-08-30T14:50:26.367Z
The word you are looking for is "meteor", and I hardly think that's what it looks like on the picture.
nataliaeire
<photography><cosmic-ray>
Could this be a cosmic ray hit on my cameras sensor (CMOS, DSLR)?
RononDex
# Could this be a cosmic ray hit on my cameras sensor (CMOS, DSLR)?

(Asked by: username_0 on 2016-07-30)

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](https://i.sstatic.net/BNcJH.jpg)](https://i.sstatic.net/BNcJH.jpg)

[![enter image description here](https://i.sstatic.net/IQMfI.png)](https://i.sstatic.net/IQMfI.png)

**Tags:** photography, cosmic-ray
> **Comments:**
> **username_1**: 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?  
> **username_0**: @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  
> **username_2**: 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.  
> **username_2**: 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  
> **username_3**: @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.  
> **username_0**: @AtmosphericPrisonEscape Aren't cosmic ray hits kind of random? If so how would a repeat of the same show its validity?  
> **username_3**: @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.  
> **username_4**: To me it looks like an airplane taking a curve (red-green-red).  
> **username_0**: @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.  
> **username_5**: Possibly a grain of dust burning up as it entered the atmosphere.  
> **username_6**: The word you are looking for is "meteor", and I hardly think that's what it looks like on the picture.  

---

## 1 answers

### Answer by username_7 on 2016-08-30. Score: 9 | Accepted answer

It's a track about 50 pixels long, at [4.1 $\mu m$ per pixel](https://photographylife.com/reviews/canon-7d-mark-ii) 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.

> **Comments:**
> **username_0**: 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**  
> **username_7**: @RononDex looks like 2230 $e^-$ is the maximum value at ISO 1600 so indeed it could be a minimum ionizing particle! Thanks!  

---

