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Full disk plus ISS solar transit - April 20

Imaging Solar
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#1 ATL Gator

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Posted 22 April 2021 - 06:15 PM

Bagged my second ISS solar transit on Tuesday afternoon. This one was almost a bust, as my original planned observing site to the west of Atlanta clouded over with less than 90 minutes remaining until the transit. Pulling up the visible satellite imagery on my laptop, I spotted an opening in the clouds that coincided with the transit path 35 miles to the south. An hour later, I exited the traffic-clogged interstate and skidded into a deserted church parking lot in Sharpsburg, Georgia (pop. 361). With the clock ticking down, I quickly set up my scope and was rewarded with some of the best views of the sun I've had in months -- I would have been happy even without seeing the ISS transit! 

 

According to transit-finder.com, the ISS was about 317 miles above the earth and traveling at roughly 16,500 miles per hour at the time of the transit. The space station's angular size was 54.21″.

 

Here's a link to a video animation of the transit: https://youtu.be/660ZWOUgM2U.

 

I was lucky to be almost directly in the center line. The video animation is slowed to approximately 1/8 actual speed as the transit itself lasted only 0.64 s.

 

The video and the attached images were captured in SharpCap 3.2 with a Lunt LS50THa and ZWO ASI178mm camera. I used a single exposure for the sun and stacked the best 60% of 1,000 frames in AS!3. I used ImPPG and Photoshop for additional processing. In the colorized image, I included a single frame from the AVI file of the transit. Although I managed to capture 32 frames containing the ISS, most were too noisy for stacking. 

Attached Thumbnails

  • 2020-04-20 full disk color with ISS web.jpg
  • 2021-04-20 full disk invert bw web.jpg

Edited by ATL Gator, 22 April 2021 - 07:09 PM.

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#2 dtmracer

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Posted 22 April 2021 - 06:48 PM

WOW!! Exceptional capture!


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#3 ATL Gator

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Posted 22 April 2021 - 07:07 PM

WOW!! Exceptional capture!

Thanks!


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#4 rigel123

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Posted 22 April 2021 - 07:44 PM

Great shot and super animation Scott!


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#5 ATL Gator

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Posted 22 April 2021 - 08:17 PM

Great shot and super animation Scott!

Thanks, Warren!



#6 TheCrimson_King

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Posted 22 April 2021 - 09:50 PM

Incredible capture! The colored image with the ISS is just one frame!?
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#7 PhotonJohn

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Posted 23 April 2021 - 12:07 AM

Great capture and images Scott. Congrats! Every transit has it's story. 


Edited by PhotonJohn, 23 April 2021 - 12:08 AM.

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#8 MAURITS

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Posted 23 April 2021 - 12:58 AM

Beautiful Scott.


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#9 ATL Gator

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Posted 23 April 2021 - 07:03 AM

Incredible capture! The colored image with the ISS is just one frame!?

Thanks! The color image is a composite of two exposures: one exposure for the sun (taken right before the transit) and one exposure for the ISS. My AVI of the transit included 32 frames of the ISS as it moved across the solar disk -- I chose one of the sharper ISS images and layered it on top of the sun image. My original plan was to stack all 32 frames to show the motion of the ISS across the sun's disk, but I had the gain set so high that most of the frames were too noisy to use -- the ISS looked like a tiny pixelated blob when I zoomed in. I'm not sure what I could have done differently to get a better result, since the speed of the ISS requires a very short exposure, and a very short exposure requires high gain. Back to the drawing board I guess! But overall I'm still happy with the result. smile.gif   

 

Great capture and images Scott. Congrats! Every transit has it's story. 

Thanks, John!

 

Beautiful Scott.

Thanks, Maurits!


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#10 Thrifty1

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Posted 23 April 2021 - 07:24 AM

Awesome job capturing this transit!!! I’m still impatiently waiting for a transit at my location.
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#11 astro rocketeer

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Posted 23 April 2021 - 08:54 AM

Beautiful shot!! Very nice! 


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#12 TheCrimson_King

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Posted 23 April 2021 - 09:57 AM

Thanks! The color image is a composite of two exposures: one exposure for the sun (taken right before the transit) and one exposure for the ISS. My AVI of the transit included 32 frames of the ISS as it moved across the solar disk -- I chose one of the sharper ISS images and layered it on top of the sun image. My original plan was to stack all 32 frames to show the motion of the ISS across the sun's disk, but I had the gain set so high that most of the frames were too noisy to use -- the ISS looked like a tiny pixelated blob when I zoomed in. I'm not sure what I could have done differently to get a better result, since the speed of the ISS requires a very short exposure, and a very short exposure requires high gain. Back to the drawing board I guess! But overall I'm still happy with the result. smile.gif   

Ahh got it. Thanks for the explanation. Out of curiosity - what was your exposure? I had a successful lunar ISS transit where 1/1600s (0.625ms) prevented motion blur. I find my normal exposure for surface features is around 2ms. Do you normally go longer for full disc with the double stack?

 

The processing on the composite is exceptional.


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#13 ATL Gator

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Posted 23 April 2021 - 02:53 PM

Awesome job capturing this transit!!! I’m still impatiently waiting for a transit at my location.

Thanks -- they're a lot of fun to chase down!

 

Beautiful shot!! Very nice! 

Thanks, Michael! 



#14 ATL Gator

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Posted 23 April 2021 - 03:04 PM

Ahh got it. Thanks for the explanation. Out of curiosity - what was your exposure? I had a successful lunar ISS transit where 1/1600s (0.625ms) prevented motion blur. I find my normal exposure for surface features is around 2ms. Do you normally go longer for full disc with the double stack?

 

The processing on the composite is exceptional.

I used 5ms for the sun and 0.33ms for the ISS. I may try a slightly longer exposure for the ISS next time, but I think 0.625ms is about as long as you can get away with before motion blur starts to become an issue. It's also possible that I'm just asking too much from a 50mm telescope to resolve a football-field sized object from a distance of over 300 miles -- especially when the object is moving at over 16,000mph. It still amazes me that it's possible to capture the ISS at all!

 

Did you image the lunar transit with your 6" SCT? I'm still waiting for a good opportunity -- there have been a few recent passes in my area but most have occurred during the daytime or when the moon is very low on the horizon.


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#15 David Boulanger

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Posted 23 April 2021 - 06:09 PM

waytogo.gif bow.gif salute.gif


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#16 TheCrimson_King

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Posted 23 April 2021 - 09:37 PM

I used 5ms for the sun and 0.33ms for the ISS. I may try a slightly longer exposure for the ISS next time, but I think 0.625ms is about as long as you can get away with before motion blur starts to become an issue. It's also possible that I'm just asking too much from a 50mm telescope to resolve a football-field sized object from a distance of over 300 miles -- especially when the object is moving at over 16,000mph. It still amazes me that it's possible to capture the ISS at all!

 

Did you image the lunar transit with your 6" SCT? I'm still waiting for a good opportunity -- there have been a few recent passes in my area but most have occurred during the daytime or when the moon is very low on the horizon.

Agreed! Pretty incredible the the ISS exists AND is in an orbit where transits happen where we live AND there is a website to predict them AND we have the gear to capture it.

 

I did use a 6" SCT for the lunar transit. Final image here: https://www.astrobin.com/agwc2o/

 

It's my best ISS transit capture to date and probably my favorite astro image I've captured so far. In total I have 8 serious attempts over the last 8 months.

  • 1 WL solar "success" with a telephoto lens, resulting image was poor from lack of focal lenth
  • 1 WL solar "success" with 6" SCT, focus was terrible (no sunspots, could only focus on limb), resulting image was poor
  • 3 WL solar failures with 6" SCT - 2 clouded out, 1 couldn't find the sun (purchased solar finder after)
  • 1 WL solar "success" with 17" ISS apparent size
  • 1 Halpha solar "success" with 17" ISS apparent size, captured same time as above, acquisition good on both but result margin because of small ISS size 
  • 1 lunar success (linked image), good result

Eventually I would like to capture a large solar ISS transit (45"+) in both WL and Halpha. I would also like to try a lunar transit where the ISS is in shadow, but I'm more excited about the solar transits right now. There is something just so rewarding about successfully capturing an event that happens at a specific time on a narrow strip of land for less than a second. The failures are humbling but make the successes that much sweeter.


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#17 peterm

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Posted 24 April 2021 - 12:28 AM

Wow that is fabulous Scott, Bravo!


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#18 lorenzo italy

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Posted 24 April 2021 - 03:25 AM

Great job Scott  waytogo.gif 
You had the courage to move at the last moment.
And luck to find clear skies so soon.
I remember that for the transit of Mercury I moved 500 km to find a clear sky ...
  Good solar observations.

 

Lorenzo


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#19 ATL Gator

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Posted 24 April 2021 - 07:57 AM

Wow that is fabulous Scott, Bravo!

Thanks, Peter!

 

Great job Scott  waytogo.gif 
You had the courage to move at the last moment.
And luck to find clear skies so soon.
I remember that for the transit of Mercury I moved 500 km to find a clear sky ...
  Good solar observations.

 

Lorenzo

Thanks, Lorenzo! This really was a case of "lucky" imaging.



#20 ATL Gator

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Posted 24 April 2021 - 08:13 AM

Agreed! Pretty incredible the the ISS exists AND is in an orbit where transits happen where we live AND there is a website to predict them AND we have the gear to capture it.

 

I did use a 6" SCT for the lunar transit. Final image here: https://www.astrobin.com/agwc2o/

 

It's my best ISS transit capture to date and probably my favorite astro image I've captured so far. In total I have 8 serious attempts over the last 8 months.

  • 1 WL solar "success" with a telephoto lens, resulting image was poor from lack of focal lenth
  • 1 WL solar "success" with 6" SCT, focus was terrible (no sunspots, could only focus on limb), resulting image was poor
  • 3 WL solar failures with 6" SCT - 2 clouded out, 1 couldn't find the sun (purchased solar finder after)
  • 1 WL solar "success" with 17" ISS apparent size
  • 1 Halpha solar "success" with 17" ISS apparent size, captured same time as above, acquisition good on both but result margin because of small ISS size 
  • 1 lunar success (linked image), good result

Eventually I would like to capture a large solar ISS transit (45"+) in both WL and Halpha. I would also like to try a lunar transit where the ISS is in shadow, but I'm more excited about the solar transits right now. There is something just so rewarding about successfully capturing an event that happens at a specific time on a narrow strip of land for less than a second. The failures are humbling but make the successes that much sweeter.

That's a fantastic shot of the lunar transit! The contrast between the illuminated ISS and the darkness of space makes for a dramatic image.

 

Your earlier email gave me an idea for how I might get a sharper image of the ISS. If I remove the double-stack filter, the image of the sun will be brighter, which would allow me to turn down the gain. I'm going to give this a try next time. There's actually a solar transit visible from downtown Atlanta this Thursday, but right now the forecast calls for rain. undecided.gif  



#21 philmor56

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Posted 24 April 2021 - 08:19 AM

Way to Hustle Scott! That's dedication indeed! (You must be practising for the eclipse!)

 

Absolutely splendid images and animation, and a great presentation too.

waytogo.gif

 

Cheers


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#22 ATL Gator

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Posted 24 April 2021 - 10:53 AM

Way to Hustle Scott! That's dedication indeed! (You must be practising for the eclipse!)

 

Absolutely splendid images and animation, and a great presentation too.

waytogo.gif

 

Cheers

Thanks, Phil!



#23 R Botero

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Posted 25 April 2021 - 02:17 AM

Fantastic Scott. Great shot, composition and story to go with it waytogo.gif

 

Roberto


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#24 ATL Gator

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Posted 25 April 2021 - 09:13 AM

Fantastic Scott. Great shot, composition and story to go with it waytogo.gif

 

Roberto

Thank you, Roberto!




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