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Interesting EEA pics

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#1 bmwscopeguy

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Posted 22 July 2021 - 08:32 AM

Hi All,

 

I was trying out my EVscope some time ago, and during an 18min exposure of NGC2903, I managed to capture a satellite or meteor going through the frame.

 

It's interesting because during the time that it took the meteor/Satellite to cross the FOV, you can see 6-7 'jags' in the trail which I assume would be indicative of the mount's tracking movements (stepped).

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#2 Mark Lovik

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Posted 22 July 2021 - 09:26 AM

One of my first computer programs (in hex .. no assembler) was writing fast circle and line writing algorithms for custom hardware.  Using a lower resolution graphics chip a straight line would show the same jags -- where the pixels would render the closest point to a straight line.  Look to see if the overall line is straight, and the deviations center on the straight line.  This may suggest the possibility the jags are pixel resolution related.



#3 davidparks

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Posted 22 July 2021 - 02:22 PM

or the satellite is spinning... smile.gif



#4 Alien Observatory

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Posted 22 July 2021 - 09:21 PM

I believe you are just "seeing" Field Rotation of an ALT/AZ Mount.  The Satellite is traveling in a direction that is not in the same Equatorial Axis of the object (NGC 2903).   The cam is exposing for a few seconds, then transferring that image to the image stack and aligning the image based of the chosen Field of View Stars.  

 

When the stacking / aligning process is occurring the cam is not taking an image.  This process can take a couple of seconds, but the field continues to rotate (maybe 5 arc sec per second).  When the next image is taken the field has rotated with the object, but not the satellite.  Thus the satellite will show a continuous zig zag motion, but a straight line durning the actual exposure.

 

You resolution is 1.7 arc sec per pixel which is quite good and the object in the image looks very good.    Pat Utah smile.gif

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#5 bmwscopeguy

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Posted 23 July 2021 - 04:43 PM

I believe you are just "seeing" Field Rotation of an ALT/AZ Mount.  The Satellite is traveling in a direction that is not in the same Equatorial Axis of the object (NGC 2903).   The cam is exposing for a few seconds, then transferring that image to the image stack and aligning the image based of the chosen Field of View Stars.  

 

When the stacking / aligning process is occurring the cam is not taking an image.  This process can take a couple of seconds, but the field continues to rotate (maybe 5 arc sec per second).  When the next image is taken the field has rotated with the object, but not the satellite.  Thus the satellite will show a continuous zig zag motion, but a straight line durning the actual exposure.

 

You resolution is 1.7 arc sec per pixel which is quite good and the object in the image looks very good.    Pat Utah smile.gif

Hi Pat,

 

Not sure if I agree. The EVscope takes 4s exposures. If what you say is correct with respect to the delay of the scope readying for the next exposure, that means that the artifact would need to have taken more than 4s seconds to traverse the FOV to even get one 'step' showing in the trail. The fact that there are 5-7 'steps' in the trail would suggest the artifact took 20-30s to traverse the FOV....doubtful. 

 

So I still think the steps are indicative of the mount's stepper drive 'stepping' multiple times during the 4 sec exposure and the transition of the artifact.

 

Cheers

Malcolm



#6 Alien Observatory

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Posted 23 July 2021 - 05:11 PM

You are most likely correct as I did not know the exposure times and I have no idea of what the stepper motor steps at (3 to 4 arc sec/ sec is typical.  If you use SkySafari you can actually track the offending satellite real time from your location on a phone, pad or computer.   Interesting that the screen capture I made from a FOV tool also has an offending satellite (maybe the same one).  Pat Utah :)




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