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Cosmic Challenge: Dissecting M101

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#1 PhilH

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Posted 01 July 2018 - 05:30 AM

Just spotting the gigantic Pinwheel Galaxy, M101, can sometimes be challenging enough. Its low surface brightness can drive suburban observers crazy, especially when we see photographs that show it so big and bright, or that it is listed as 8th magnitude. It all comes down to surface brightness, or more accurately, lack of surface brightness. Seeing the dim glow of the galaxy's small core, or the even dimmer glimmer of the surrounding spiral arms, can take a concerted effort. But with time and patience, M101 is visible, with difficulty, through 50-mm binoculars even given a suburban sky with a naked-eye limiting magnitude of perhaps 4.5.

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#2 TieDyeAstronomer

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Posted 03 July 2018 - 09:38 PM

But with time and patience, M101 is visible, with difficulty, through 50-mm binoculars even given a suburban sky with a naked-eye limiting magnitude of perhaps 4.5.

Hi, Phil! What Bortle number would you estimate those kinds of skies at? I live in the city under hard Bortle 9 skies, but reach limiting magnitudes of ~5.0-5.5.

 

I set up my 15x70 binoculars + parallelogram mount last night to search for M101, but got no convincing hints. I was able to barely, with effort, see M51, and in a brief moment of clarity saw a mag 11.5 star pop a time or two. The transparency was not the best, but good for summer (I live in Houston so there's tons of gulf moisture). The skyglow was bright enough that I was able to see plainly into the deepest shadows under the trees 50' away, and the sky was the color of a planetary nebula overhead and in the direction of Ursa Major, simultaneously blue and green. Towards the horizon or my many light domes it turned tan. I will keep trying for M101 under hopefully better conditions.

 

Clear Skies!

Lauren Herrington



#3 Chesterguy1

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Posted 04 July 2018 - 09:32 PM

I’m sure under pristine unpolluted skies that M101 is visible with instruments under 100mm.  I was checking my observer’s log from last year around this time and viewed the sketch with my 8” at about 70x.  It was a barely discernible irregular grey patch only marginally lighter than the background. More magnification did not produce meaningful detail and certainly nothing like the structure Phil sketched with his 18”.  I live in a Bortle 5 zone and took an SQM reading of the area which yielded a reading of 20.35.  I typically have good-excellent transparency.


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#4 TieDyeAstronomer

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Posted 05 July 2018 - 07:48 PM

Hey Chesterguy1! Thanks for sharing your report!

 

I’m sure under pristine unpolluted skies that M101 is visible with instruments under 100mm.

 

Definitely! I've been able to see it quite "easily" (for a deep sky object) in my 15x70 binoculars from a Bortle 3-4 site, and one where the big light dome is to the North too, so not the best for M101. But having such a low surface brightness, it sure does get wiped out fast. I bet it would be a bigger struggle from my club's Bortle 4.5 dark site.

 

Clear Skies!

Lauren Herrington



#5 Chesterguy1

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Posted 06 July 2018 - 07:58 AM

Hi Tie:

 

For me, it's always a better target this time of year:  high in the sky, more north/northwest and away from the small light dome of my city, which for me is NE.  It's still a tough target and even with my 15" it reveals little structural detail from my admittedly suburban zone.  It is, of course, much easier to find with the 15" (although I would never classify it as easy from my locale).  What I can see readily--but is more elusive in the 8" are the nearby NGC galaxies, 5473 and 5474.  I cannot see 5477.  Thus, the galaxies Phil sees within the structure of M101 are simply not possible unless I go to a much darker site.

 

Gogiboy


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#6 Dave Mitsky

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Posted 07 July 2018 - 02:27 PM

I can sweep up M101 fairly easily with my Celestron 8x42s from a really good dark site.

 

Dave Mitsky



#7 Dave Mitsky

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Posted 07 July 2018 - 02:32 PM

M101 and its HII regions can be quite spectacular through a large aperture from a pristine site.

 

http://www.robgendle...m/M101text.html

 

http://messier.seds.org/m/m101.html

 

Here's an image that I captured years ago using the BRT.

 

M101 (The Pinwheel Galaxy)
2/22/2013
14" f/11 Celestron C14 SCT working at f/5.3
FLI MicroLine CCD camera
100 seconds
Bradford Robotic Telescope
http://www.telescope.org/
Tenerife, the Canary Islands

 

Dave Mitsky

Attached Thumbnails

  • M101 2-22-2013 Reprocessed CN 640.jpg

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#8 Bill_H

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Posted 13 July 2018 - 08:45 PM

Great article, Phil!


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