[and why some GC's can be difficult to see when their noted magnitude says they are "bright"... same with galaxies...]
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.
Edited by maroubra_boy, 10 June 2021 - 11:25 PM.