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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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#11 jayrome

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Posted 31 May 2019 - 09:13 AM

I'm really looking forward to heading out to my dark sky site in the next couple weeks; just picked up a 10mm Hyperion eyepiece which I'm hoping is going to give me better views of M51 than the stock 26mm Meade that came with the scope + the 2X 2" barlow


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#12 Araguaia

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Posted 31 May 2019 - 10:46 AM

I had my first look at M51 this season 3 nights ago, as it peaked at just over 30o above the northern horizon.  It was very dark as usual, but transparency down low was below par.  Disconcertingly, I could not see the spiral arms no matter how hard I tried, at any power.  The best I got was a ring around it, that did not seem to attach to the central core.

 

(note: I could easily make myself "see" the spiral arms if I was careless, especially at 109x, the power at which I have most often observed this galaxy.  This is how averted imagination works, and it is good practice to learn to control it.  I kept conjuring up the "image" of the arms, and of course, every time I did so they attached to the core at a different position, etc., giving away their false nature).

 

Two nights ago I was out again, and this time transparency was up to standards for this time of year.  The spiral arms were clear and detailed, and with averted vision I could see the bridge.  M101 was looking very good too, even lower in the sky.

 

From this I had the lesson reinforced that transparency is the key to observing detail in galaxies - perhaps more so than even light pollution.  Haze certainly makes any LP much worse.


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#13 antariksha

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Posted 16 June 2019 - 01:42 PM

M51 is one of my favourite objects. I have a small house, 160 km off Mumbai, India, which is fully dedicated for my hobby. With my 18", F4.5, the view of M51 is stunning. I normally begin with my Televue 21mm ethos and then switch to 11mm Delite. Delite gives much better details. However, I have found that using 21mm earlier and then using 11mm, the eyes get adjusted better and arms are visible better.


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#14 Volksaholic

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Posted 18 June 2019 - 05:33 PM

This is timely because my wife and I just bought our first telescope (8" Dob) and I'm trying to learn how to find objects. I've looked for M51 a couple of times from the back yard and failed, but last weekend there were high clouds that were making even a few bright objects a little hard to see. I know an 8" reflector doesn't technically qualify for the challenge, but it's a good exercise for me and if I can find it with the telescope maybe I'll take a crack at seeing it with my binoculars or photographing it too.

Paul



#15 antariksha

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Posted 20 June 2019 - 12:27 AM

Paul, with 8", you would definitely see M51 as fuzzy spot and NGC 5194 smaller fuzzy spot. The spiral arms may not be seen possibly. But I am sure you will have a satisfying view.



#16 Dave Mitsky

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Posted 20 June 2019 - 09:00 PM

Here's the section on M51 from my post at https://www.cloudyni...mers/?p=4592919

 

M51 (the Whirlpool Galaxy)

 

M51 (NGC 5194, integrated magnitude=8.4, surface brightness=12.6 magnitudes per square arcminute), a type SA(s)bc pec face-on spiral galaxy, and its irregular companion M51b or NGC 5195 (magnitude 9.6, surface brightness=13.1 magnitudes per square arcminute) are perhaps the most prominent example of an interacting pair of galaxies. They are best seen in the spring.

 

Due to the work of Lord Rosse In 1845, M51 was the first galaxy to be recognized as having a spiral shape. Of course, M51 was merely a "nebula" at that time, which was long before galaxies were determined to be objects external to the Milky Way.

 

M51 and NGC 5195 may be part of the M101 group of galaxies. Three supernovae have occurred in M51: SN 1994I, SN 2005cs, and SN 2011dh.

 

To star-hop to the Whirlpool Galaxy, proceed southwest from Alkaid (Eta Ursae Majoris), the final star in the Big Dipper's handle, to the fifth-magnitude star 24 Canum Venaticorum. Continue southwest to an isosceles triangle of seventh-magnitude stars. M51 and NGC 5195 lie just to the south of the triangle, approximately 3.5 degrees from Alkaid and 1/4 of the way to Cor Caroli (Alpha Canum Venaticorum).

 

Star-hops to M51 can be found at the following sites: 

 

http://www.skyledge....ssier51-hop.htm

 

https://www.britastro.org/node/12846

 

http://adsabs.harvar...JRASC..93..253M

 

Telrad finder charts for M51 are available at the following sites: 

 

http://www.custerobs...cs/messier2.pdf (map 5)

 

http://www.star-shin...charts/m051.htm

 

For further information on the Whirlpool Galaxy, consult these sites:

 

http://messier.seds.org/m/m051.html

 

http://www.universet...997/messier-51/

 

http://www.cloudynig...hp?item_id=1073

 

http://www.daviddarl...ol_Galaxy.html 

 

http://www.nightskyi...irlpool_galaxy/

 

https://www.messier-...irlpool-galaxy/

 

http://www.backyard-.../top100/08.html

 

https://tonyflanders...rly-spring/#M51

 

http://www.dreistein...=A&id=77224&on=

 

Dave Mitsky


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#17 Araguaia

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Posted 21 June 2019 - 05:23 AM

Last night M51 was looking good!  I could see both spiral arms at all powers, from 51x to 277x.

 

The bridge between the galaxies, however, was only visible in AV.  It is a lot fainter than the main arms.



#18 Volksaholic

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Posted 23 June 2019 - 05:02 PM

I tried and failed to find M51 again last night. I had some new-to-me eyepieces to try out, as well as a Dioptrx so I can try viewing without my glasses. I suspect the sweet lens to initially find it will be a Nagler Type 4 22mm that got its first trial last night. I also bought a Nagler Type6 11mm but from what I've read I think I should start with the 22mm (I welcome correction if that's wrong). I was viewing from my back yard and the skies were clear but it is on the East bench of Salt Lake City so there's a bit of light pollution. I'm pretty sure it's me and not the 'scope that's failing. I suspect that once I see it and know what I'm looking for that I'll be able to make it out with conditions like we had last night. I think the Dioptrx is going to help too because I was having a lot of trouble with the kit eyepieces and my prescription glasses. My astigmatism is bad enough (-3.25 in both eyes) that I can't even really focus the telescope without correcting for it. 

I love the resources posted above... I'll see if they help me nail it down. I'm looking forward to my next opportunity to head to South or West out of the city now that I've got better eyepieces and a little better understanding of how to find my way around. 



#19 Inkswitch

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Posted 24 June 2019 - 08:35 PM

I tried and failed to find M51 again last night.

 

For some reason M51 is also a problem for me to find.  I have seen it many times and had difficulty finding it many times.  I think, at least for me, it is because it is so far North and directions like East and West become less defined the closer you get to the pole.  Or maybe I am just overthinking it, I always seem to go the wrong way from Alkaid at first, then I eventually get my bearings and find it.  It is so close to a prominent star that you would think it would be easier.



#20 Araguaia

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Posted 25 June 2019 - 11:28 AM

There are two stars of about magnitude 5 just to the west of Alkaid. 

 

If you imagine that there was a third star, forming a right triangle with the other two, so that the right angle corner points to Alkaid, and the leg to the imaginary star is just a bit shorter than the leg between the two real mag 5 stars, M51 is at the position of this "imaginary star".

 

If you look at a star chart you will know what I mean.



#21 Dave Mitsky

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Posted 25 June 2019 - 03:37 PM

I removed the dead links from post #16 and added ones that work.

 

Dave Mitsky




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