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Globular Cluster marathon from under light polluted skies - a heck of a lot are visible!

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#1 maroubra_boy



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Posted 10 June 2021 - 11:18 PM

[and why some GC's can be difficult to see when their noted magnitude says they are "bright"...  same with galaxies...]


Hi all,


In April last year I did a planetary marathon sketching as many PN's as I could in a night from my home in Sydney, Australia.  As it turned out I needed to do this over two nights as just so many PN's were visible.  A good mate of mine Aperturefever started a thread about it here so I won't post pics of the pieces again.


Inspired by the experience I had, I looked at doing the same with globular clusters.  The difference here though was the PN marathon I had no dew issues to compromise my paper.  With the night I was able to get a start on the GC's, dew was a big problem and I finally had "first sketch" of the new heated sketch pad I created for myself.  Enough to say that this new contraption worked like a charm!  I spent roughly two hours with each sheet of paper doing the four individual sketches on each, and the paper not only stayed bone dry but also didn't soak up any water and didn't soften or expand.  BLOOMING TRIUMPH for my sketching capacity!    


As with the PN marathon, I again used my 9" Santel Maksutov.  As it turned out I only needed the one eyepiece for these works (unlike with the PN's), and I deliberately kept it "simple" using a 30mm plossl.  We can get caught up in our fancy R2D2° eyepieces that we can overlook the transmission capabilities of more modest eyepieces and that BIG AFOV is not everything.  Actually for me not having a big AFOV made the sketching an easier exercise which was desirable for me this night.  This scope-EP combination gives 100X (give or take a bee's willy).


One thing was apparent to me with these GC's.  I had compiled a list of visible GC's where I noted their visual magnitude and size.  While all were considerably larger than Jupiter in terms of angular size, their ease of visibility was certainly much more challenging with the fainter ones.  This understandably follows because their listed magnitude is for a pinpoint of light of its collective light, and when this light is spread out over a large area, the actual true brilliance of the GC can go out the window!  And unlike PN's, I cannot use a filter to help show them up more easily.  So while I sketched only 8 GC's this night I had actually aimed the scope at 11 separate GC's and failed to see three of them because their surface brightness under my urban light polluted skies just couldn't show them.


One GC in the lot in particular demonstrates this.  NGC 6101 was visible as a very faint soft round glow.  It was not immediately evident when I first looked through the scope and took a bit of doing to be certain that I had found it.  6101 is listed as being magnitude 9.15 (I've been able to see mag 10 galaxies through this scope) and its size is 5', roughly 12 times the diameter of Jupiter.  This meant that it was going to be a faint sucker from my home.  I could not resolve any stars in 6101.


M80 was a bit of a novel creature.  With an angular size twice that of NGC 6101, and nearly two whole magnitudes brighter, its structure was completely different.  Through the eyepiece M80 appeared smaller than 6101 and it was very intense towards its almost stellar-like core, whereas 6101 was more even in its light distribution with no core brightening.  With averted vision I was able to resolve M80, and it took a bit of doing.


And M4, OMG!  What a stunner!!!!


I could have continued with the marathon beyond what I had put down, but it was starting to get cold with my feet were frozen and I just had to call it quits.



Scope:  9" Santel Maksutov, f/13.5

Gear:  30mm plossl, 100X, 0.5° TFOV

Location:  Sydney, Australia

Date:  6th June 2021

Media:  White soft pastel and charcoal on A4 size black paper.

Attached Thumbnails

  • GC marathon 1 LR.jpg
  • GC marathon 2 LR.jpg

Edited by maroubra_boy, 10 June 2021 - 11:25 PM.

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#2 greenstars3



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Posted 11 June 2021 - 12:50 AM



Very cool, globs are my favorite




ps I like to track them down with my 180 Mewlon, then look at them with a 15" dob and a 32 Plossl is a great eyepiece (I don't have a 30)

Edited by greenstars3, 11 June 2021 - 12:53 AM.

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#3 Bill Barlow

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Posted 11 June 2021 - 11:45 AM

Love looking at M4 through apertures of 8” or more and the bright/dense band of stars cutting through the middle.  Very nice sketches by the way!  


Edited by Bill Barlow, 11 June 2021 - 11:46 AM.

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#4 payner



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Posted 11 June 2021 - 11:55 AM

Great sketches and project, Alex. I greatly enjoy globulars myself and are good targets for the more light polluted skies than most DS objects (along with OC and PN).



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#5 Dave Mitsky

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Posted 11 June 2021 - 08:14 PM

Love looking at M4 through apertures of 8” or more and the bright/dense band of stars cutting through the middle.  Very nice sketches by the way!  


Here's an image of M4 that I captured thanks to what was known at the time as the Bradford Robotic Telescope that displays that globular cluster's "bar of stars".

Attached Thumbnails

  • M4 BRT May 2009 Reprocessed.jpg

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#6 jjbroomco


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Posted 12 June 2021 - 05:03 PM

Cool project, thanks for sharing. M4, M13, and especially M22 are my favorites. They look even more amazing under dark skies (Bortle 4 and lower).
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#7 DSOGabe



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Posted 12 June 2021 - 05:54 PM

I observe under Bortle 8 skies and still have had fairly good success with GCs. Next month will end my 12 month open cluster marathon and I'm planning on focusing on globulars for the next 12 months . 

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#8 maroubra_boy



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Posted 12 June 2021 - 07:44 PM

Thanks for the kind words everyone 😄

One thing I have wanted to stress in my post is how GC's along with PN's and yes OC's too, are the urban observer's El Dorado - the hidden treasure. The replies here go to reinforce this. Galaxies & big showy nebulae may be the glamour pinups of astro, but under urban skies they just don't cut it.

If you are new to astro, I also want to stress that GC's, PN's & OC's are not the poorer cousins of DSO's but hold their own intrigue, variation & physics. Some (if not all GC's) are the remnant cores of galaxies that the Milky Way swallowed up long, long ago. Many date to among the oldest objects in the Universe. Many also harbour black holes (Omega Centauri & M13), even multiple black holes (M22 {if I remember correctly has 2}). Others present challenges to astronomers and cosmologists to explain their appearance/composition as they do not conform to the GC theories that have been formulated - & in turn question more fundamental ideas on the formation of the Universe from the very start.

PN's are the antithesis of what we see - the doom of everything that has been formed. Some are the end of average Joe stars like our Sun. Others are the precursor stumblings of super massive stars about to go supernova (Thor's Helmet & the Homunculus) and are critical in our understanding the mechanics of stellar evolution, including one way of the formation of black holes.

OC's I'll leave to you to work out their appeal & nerd.

While we as individuals may struggle to see the appeal of these objects, for outreach under light polluted skies these are our El Dorado realised. It is then up to us on how to spin them so we can excite participants why these are as sexy (seductive if the CN censor edits the secksy word... 😄) & show pieces when galaxies & nebulae are out of the question.


Edited by maroubra_boy, 12 June 2021 - 07:47 PM.

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#9 Voyager 3

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Posted Yesterday, 08:07 AM

But when someone talks about diamonds on velvet background , it is mostly open clusters or rich star fields !


Back to GCs , I must say , even from light pollution , globulars are just fuzz clouds untill the magnification is high to very high . Untill 150-200X globulars don't come to life in ANY aperture . So next time you are out for globulars , don't forget to take your short FL eyepieces/Barlow . Don't believe me ? Try a ≈2mm exit pupil and then a ≈1mm exit pupil . This is especially true in the case of smaller telescopes . 

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