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Uranus on November 17th and 23rd, images + albedo

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#1 CPellier

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Posted 03 January 2021 - 07:09 AM

Hi all, 

Here are some images of Uranus taken under very good seeing last November (many good nights back then, not one since!).

The bright North polar region is progressively occupying a higer part of the disk as the pole is slowly tilting towards us, and is now within reach of the resolution of small telescopes (I saw one taken with a 8" recently). I wonder how it will change the color of the planet, because it is definitely less green than the rest of the globe...

It is easy to see in RGB, much more with Baader RG610, but barely detectable with a Johson V filter.

I present as well a partial photometric work performed on Nov. 17th. That night, I made a complete photometric observation for Mars (I did not post that here), with reference stars taken and the use of Johson UBVRI filters. The stars did not worked well to make the photometry of Uranus since it is found higher in the sky, so I used more precise data obtained last year by spectroscopy. The result is a four point double spectrum that draws the albedo difference between the two regions of the planet, the bright nothern pole, and the darker greenish rest of the globe.

The series from the 17th also shows that the polar region is now detectable in green light. 

With best wishes to you all for 2021!

Christophe

Attached Thumbnails

  • U2020-11-23_21-54_rgb_cp.png
  • U2020-11-23_22-19_rir_cp.png
  • U2020-11-23_22-41_v_cp.png
  • U2020-11-22_23-09_b_cp.png
  • U2020-11-17-albedo_cp.png
  • U2020-11-17_22-39_b_cp.png
  • U2020-11-17_22-53_v_cp.png
  • U2020-11-17_23-20_r_cp.png
  • U2020-11-17_23-34_i_cp.png

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#2 Couder

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Posted 03 January 2021 - 09:57 AM

Wow


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#3 Stellar1

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Posted 03 January 2021 - 10:02 AM

Amazing work!



#4 CPellier

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Posted 03 January 2021 - 03:40 PM

Thanks!



#5 Tulloch

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Posted 03 January 2021 - 04:35 PM

Really impressive Christophe, thanks for posting.

 

I've now gone back over my own Uranus images from Aug - Nov, but I cannot see any signs of the polar region brightening with my 9.25" and ASI224MC. If the weather cooperates, I might have another go in the next month, Uranus is still in a pretty good position right now. 

 

Any tips for catching this polar region? For instance, I notice you de-rotated a 20 minute video for your images.

 

Thanks, Andrew


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#6 CPellier

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Posted 04 January 2021 - 11:16 AM

Really impressive Christophe, thanks for posting.

 

I've now gone back over my own Uranus images from Aug - Nov, but I cannot see any signs of the polar region brightening with my 9.25" and ASI224MC. If the weather cooperates, I might have another go in the next month, Uranus is still in a pretty good position right now. 

 

Any tips for catching this polar region? For instance, I notice you de-rotated a 20 minute video for your images.

 

Thanks, Andrew

Thanks Andrew. Apart of excellent seeing and a perfectly aligned telescope (this is for any planet, but any collimation error is merciless for the two ice giants) to easily capture the polar region you need a red/IR filter, of wide passband to avoid a too dim image. The Baader RG610 or the Astronomik BP642 are perfect for it, the Baader IR685 brings more contrast but at the expense of the resolution.

It is also wise to make very long videos, indeed. The polar region is now wide enough to appear with 5 to 10 mn, but 15 to 20 is better...


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#7 leoyasu

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Posted 04 January 2021 - 03:12 PM

Impressive shots Christophe! I tried with an IR850 filter without success but your results encourage me to try next year with some IR600ish filter plus the ADC. My photos had the blue channel all misaligned. I also see that it says AltAz derotation, I have a 14 "dobson with Alt Az tracking. Can you explain the technique used? Thanks!



#8 CPellier

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Posted 04 January 2021 - 04:25 PM

Impressive shots Christophe! I tried with an IR850 filter without success but your results encourage me to try next year with some IR600ish filter plus the ADC. My photos had the blue channel all misaligned. I also see that it says AltAz derotation, I have a 14 "dobson with Alt Az tracking. Can you explain the technique used? Thanks!

Thanks Leoyasu,

The IR850 is much too dim for that planet ; you can see on the below spectra of Uranus and Neptune that after 850 there is nothing left as light...

The correction of field rotation is performed under WinJupos (and partially, for the bigger planets, with AS3). You can read a presentation I made of the technics two years ago here smile.gif

Attached Thumbnails

  • 2019_uranus-neptune_spectra_cp.png

Edited by CPellier, 04 January 2021 - 04:26 PM.

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#9 CPellier

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Posted 04 January 2021 - 04:31 PM

You can read as well the use of filters for Uranus explained by spectroscopy !


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#10 JohnEEvans

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Posted 04 January 2021 - 05:04 PM

Very interesting!

#11 CPellier

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Posted 05 January 2021 - 02:46 AM

thank you :)



#12 Quinnipiac Monster

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Posted 05 January 2021 - 06:24 AM

Amazing post, thank you for this. 



#13 CPellier

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Posted 05 January 2021 - 12:01 PM

Thanks!



#14 leoyasu

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Posted 05 January 2021 - 03:07 PM

Great info! Somehow I keep forgetting adding your site to favorites, well no more grin.gif


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#15 CPellier

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Posted 05 January 2021 - 04:50 PM

Many thanks ;) 



#16 Tyson M

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Posted 13 January 2021 - 12:20 AM

Superb!!



#17 CPellier

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Posted 13 January 2021 - 11:57 AM

Thanks :)



#18 Quaternion

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Posted 21 January 2021 - 01:29 PM

Incredible work Christophe !  I may have missed my good seeing nights on Uranus for this year...


Edited by Quaternion, 21 January 2021 - 01:29 PM.

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#19 CPellier

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Posted 03 February 2021 - 04:48 AM

Thanks Quaternion, sorry I missed your answer !




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