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Cosmic Challenge: M51's spiral arms

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#1 PhilH

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Posted 30 April 2019 - 07:55 AM

Of the thousands of spiral galaxies visible through backyard telescopes, one stands above the rest in terms of visual interest: M51, the famous Whirlpool Galaxy in Canes Venatici. Everything adds up in M51's favor. We are seeing it very nearly face-on, its spiral arm halo is bright and peppered with star clouds and vast regions of nebulosity, and it brings with it a friend in the form of a smaller companion galaxy that can even be seen through giant binoculars.

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#2 Astrojensen

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Posted 01 May 2019 - 02:05 AM

I can attest that the arms really are visible in a 4", at least a 4" high-quality refractor. This happened to me recently on a very clear night. I didn't expect it at all and caught me completely by surprise. I'm not quite sure of the NELM, as I never checked, but M13 was dimly visible to the naked eye. The scope was my 4" f/11 ED and the magnification was a fairly high 90x with a 9mm ES100 and an (approximately) 0.7x compressor. I can confirm that the dark bands became visible first and then the brightest parts of each arm. In 2012 I made a drawing of M51, using a 6" f/8 achromat and it shows essentially what I saw with the 4":

 

med_gallery_55742_324_1407448826_25253.j

 

The overall shape of the galaxy - including the bridge - can be seen in a much smaller instrument. Here's a drawing I made in 2011 with my 63mm Zeiss:

 

med_gallery_55742_324_1407446950_23133.j

 

 

Clear skies!

Thomas, Denmark


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#3 Araguaia

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Posted 01 May 2019 - 06:42 AM

The arms are easy direct vision features through a 12" scope, even with M51 rising to barely 30 degrees as it does here.  The bridge to NGC 5195 requires averted vision, except on the most transparent nights.  


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#4 John O'Hara

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Posted 01 May 2019 - 06:39 PM

I've found sky darkness and seeing are important in viewing spiral structure in M51.  I've seen decent structure in my old 6" f/8 A-P at Cherry Springs State Park, Pennsylvania.  My best view was in Florida at Shell Mound Park near the Gulf Coast hamlet of Cedar Key.  The sky there was about Bortle 2 at the time, and the seeing rock steady, possibly the best seeing I've ever experienced.  The view was through my 12.5" f/5 Teeter Dobsonian at 227x and was spellbinding.  (However, that's a larger scope than the range for this challenge.)

 

Thomas' experience with a 4" has my wanting to take out my 100 SW ED.  The night would have to be a good one!  I could try it in my 2.4" Swift refractor, but I'm sure it will fall short of Thomas' Zeiss (I'm sure his skill is a factor as well!).


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#5 Astro Canuck

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Posted 02 May 2019 - 02:50 PM

This was what m51 looked like as I saw though my open 8th floor apartment window

in light polluted Halifax last year.   I may try again this year when it is better placed.


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#6 Arcticpaddler

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Posted 03 May 2019 - 06:43 PM

M51, along with M101, is one of the few galaxies where you can actually detect the spiral structure visually.  I have seen hints of the spiral structure several times through my 8-inch SCT from my backyard here in NE Minnesota, Bortle 3 skies.  I would guess that they would be even more obvious in the Bortle 2 and 1 conditions an hour to the north.


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#7 John O'Hara

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Posted 06 May 2019 - 04:14 PM

Very sad news, indeed concerning Tom.  He was too young and will definitely be missed.  We've been loosing to many lately in our ranks.  We're such a small community really.



#8 PhilH

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Posted 08 May 2019 - 03:21 AM

Very sad news, indeed concerning Tom.  He was too young and will definitely be missed.  We've been loosing to many lately in our ranks.  We're such a small community really.

True, John.  Sadly, true.



#9 Phillip Creed

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Posted 10 May 2019 - 11:43 AM

I used a pair of 4" scopes in the form of a set of 25x100 binoculars from Big Bend National Park.  Under that Bortle Class 1 sky, it wasn't that difficult to see the spiral arms in M51.  Like others have mentioned, sky conditions are CRITICAL.

Best view was throw Bill Prewitt's 20" dob from Spruce Knob, WV.  That was AMAZING.

Clear Skies,

Phil


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#10 Augustus

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Posted 15 May 2019 - 06:51 AM

I used my 6" f/4.3 last year at Stellafane and was able to see the arms relatively easily. At home (Bortle 5 or 6) the arms can just be seen with my 12" or a 10".


Edited by Augustus, 15 May 2019 - 08:05 AM.

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