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Europa casting a strange shadow on Jupiter

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#1 Rac19

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Posted 14 August 2019 - 07:28 PM

Last night I wanted to capture an image of Europa casting a shadow in Jupiter, Seeing conditions were terrible but I went ahead anyway. Europa was barely viable in live view but I could see a strange "flare" to the "right" of the very flickering dot that was Europa. There was just a hint of its shadow on Jupiter, if you used your imagination

 

The attached image is heavily over-processed in RegiStax but the "flare" seems to be casting a shadow/ I don't know what to make of it.

 

 

 

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#2 rkinnett

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Posted 14 August 2019 - 07:45 PM

Water-ice plumes!

 

Kidding, sorry.  I saw a similar effect from the shadow of Io a few weeks ago, but it disappeared the second time through Autostakkert with better selection of alignment points and reference frame.

 

Looks like you got pretty good detail on Jupiter though.  Was that with your asi1600?  Which Powermate?  It's a good result for a "went ahead anyway" session :)


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#3 Rac19

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Posted 14 August 2019 - 08:12 PM

Water-ice plumes!

 

Kidding, sorry.  I saw a similar effect from the shadow of Io a few weeks ago, but it disappeared the second time through Autostakkert with better selection of alignment points and reference frame.

 

Looks like you got pretty good detail on Jupiter though.  Was that with your asi1600?  Which Powermate?  It's a good result for a "went ahead anyway" session smile.gif

Yep, I used the ASI1600MC with the PowerMate 2,5x. The results are much better on a good night. I used AutoStakkert for stacking then RegiStax for wavelets, applied in the extremesmile.gif. I am trying to figure out whether the flare is real or just a stacking artifact, I guess that the same stacking effect could occur with the shadow as well as the moon. The ghost outlines of Jupiter to teh right might be clue.

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#4 TOMDEY

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Posted 14 August 2019 - 09:20 PM

Possibility A: Peculiar V-shaped shadow.

Possibility B: Processing artifact.

 

Conclusion: Entirely artifactual.    Tom



#5 Rac19

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Posted 14 August 2019 - 10:59 PM

The more I think about it, option B is far more likely.

#6 CPellier

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Posted 15 August 2019 - 06:05 AM

Another hypotesis: miscollimation+ maybe some astigmatism or trefoil... you may check the Airy pattern to be sure :)


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#7 Rac19

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Posted 15 August 2019 - 06:55 AM

Another hypotesis: miscollimation+ maybe some astigmatism or trefoil... you may check the Airy pattern to be sure smile.gif

I am reasonably sure that collimation is good but I will check it next time. Europa was only fleetingly visible in live view and the "tail" was in evidence.



#8 Selenite

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Posted 15 August 2019 - 12:50 PM

Jupiter's moons have horns when the primary mirror of an SCT is warmer than the rest of the scope. You can get rid of them by letting the scope cool down longer and/or heating the corrector. I don't remember seeing this during a shadow transit though so I'm not sure how a heat plume would affect the shadows.


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#9 KiwiRay

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Posted 15 August 2019 - 01:14 PM

See this post on artifacts around Tethys - I think the cause of your strange shadow is the same.

 

https://www.cloudyni...tion/?p=9573565

 

I see this all the time with Jupiter's moons, except for the shadows it appears dark instead of light.  Always the same triangular pattern, but often with uneven brightness of the vertices of the triangle.  Someone with a better understanding of optics than me would have to explain it.  It's not a processing artifact, though, as it can be seen onscreen if you increase the exposure enough.



#10 Rac19

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Posted 15 August 2019 - 05:25 PM

See this post on artifacts around Tethys - I think the cause of your strange shadow is the same.

 

https://www.cloudyni...tion/?p=9573565

 

I see this all the time with Jupiter's moons, except for the shadows it appears dark instead of light.  Always the same triangular pattern, but often with uneven brightness of the vertices of the triangle.  Someone with a better understanding of optics than me would have to explain it.  It's not a processing artifact, though, as it can be seen onscreen if you increase the exposure enough.

Yes, the triangular pattern was fleetingly visible near the moon in real time, therefore not due to stacking or wavelet artefacts. It is to be expected that this effect would be integrated (summed) during stacking and appear almost to be something real. What is a little puzzling is that there appears to be a matching shadow. The shadow itself was much less visible in real time and its shape was not discernible.

 

I did wonder about collimation, but it looked reasonable during initial focusing. I will look more closely next time.

 

I set out with intention of capturing a clear, detailed image as per post #3, with a sharp, black circular shadow, but it just wasn't to be on the night.

 

Thanks for the link, I will read it with interest.



#11 KiwiRay

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Posted 15 August 2019 - 06:20 PM

This is an animation including Europa's shadow transit from two years ago.  Look closely and you can see at least two of the three spots move with the shadow across Jupiter.

 

https://c1.staticfli...c85aa54d7_o.gif

 

I never quite get that sharp shadow you were also looking for because of this.



#12 Tavi F.

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Posted 15 August 2019 - 06:36 PM

It is coma, due to missalignment or high inherent coma of the system if an ADC was used (the ADC forces the light path to be off-axis).




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