View Full Version here: : The Third Brightest Globular: NGC 6752 in Pavo
07-05-2012, 08:32 PM
I continued imaging while the Moon steadily increased its influence during last week... I had to limit myself to fairly bright targets so I stuck to globulars. The following image was taken under an unforgiving 94% illuminated Moon and I had to battle with some strong gradients but the end result proved much better than I could hope for, so here is the third brightest globular, NGC 6752 in Pavo:
http://www.pbase.com/rolfolsen/image/143154105/original (Hi res version 751KB)
10" f/5 Serrurier truss Newtonian
QSI 683wsg with Lodestar guider
This image is a crop of about 80% of the full frame, there was a nasty reflection from the Moon near the top so a slight crop was called for. I also did a thorough collimation prior to taking this image and think I have eliminated most of the coma now. The FWHM was hovering around 2.0"-2.5" which is a bit less than in my previous images so that was promising.
Despite the moonlight there are even a handful of faint background galaxies showing, see if you can spot them :P
BTW I actually really enjoy the refractor like views that the wire spider provides - look at that, not a diffraction spike in sight! Only an ever so slight hint of them on the 7th magnitude star HD 177999 near the centre :D
Hope you enjoy this view of one of the more overlooked of the bright globulars (click image link above for best quality version). Comments and critique is most welcome .
07-05-2012, 09:31 PM
Very nice result, Rolf. The wire spider works really well!
07-05-2012, 09:47 PM
That's a good NGC6752 Rolf. Lovely rich colours.
07-05-2012, 10:07 PM
Nice one Rolf
07-05-2012, 10:29 PM
Nice image Rolf all the normal parts are spot on, the only thing that isn't really to my flavour is the electric blue stars and the deep orange. Flavour is what one makes it though!
07-05-2012, 10:30 PM
Very nice. I love these golden stars in these globs. I guess they show that they are really old stars.
07-05-2012, 11:40 PM
That's a great pic.
You have such fine detail & plenty of colour.
07-05-2012, 11:58 PM
Well done Rolf - great detail. My only comment is I'd like to see the stars a lot brighter, less colour - they are suns.
One of the great objects - yet not so well known.
Good to see some images! :)
Q. When giving the length of exposures (24:8:8:8) ... is that the total of the stacks or a length of each single image? Just trying to work out how long to expose for...
08-05-2012, 08:54 AM
Excellent result Rolf, you are on a roll with these globs :thumbsup:
08-05-2012, 09:14 AM
beautiful image Rolf, the different coloured stars make this a outstanding view. Thanks.
08-05-2012, 10:00 AM
Wow, stunning as usual Rolf!
08-05-2012, 12:55 PM
Very nice, Rolf, colors are very saturated and add lots of beauty to the picture IMHO!
? I didn't know it, what is the ranking? I supposed it was Omega/47 tuc/M13..
Another question: I don't usually image with LRGB if the moon is up, apart from gradients do you find a big difference comparing to RGBs you get on moonless nights?
08-05-2012, 01:58 PM
Nice work Rolf. Composition, star colours and resolution all great.
08-05-2012, 02:57 PM
Ah huh! ;)
We have 7 of the top 10 brightest Globulars well down in the southern hemisphere incuding the three brightest! :D
1) Omega centauri in Centaurus Mag 3.9 Dec -47
2) 47 Tuc in Tucana Mag 4.91 Dec -72
3) NGC 6752 in Pavo Mag 5.4 Dec -59
4) M13 in Hercules Mag 5.8 Dec +36
5) NGC 6397 in Ara Mag 5.9 Dec -53
6) M22 in Sagittarius Mag 6.17 Dec -24
7) NGC 2808 in Carina Mag 6.2 Dec -65
8) M3 in Canes Venatici Mag 6.2 Dec +28
9) M15 in Pegasus Mag 6.2 Dec +12
10) M55 in Sagittarius Mag 6.3 Dec -31
NB. Of these 10, only really M13 is not well placed for viewing from mid southern latitudes (although still a good view when crossing the meridian from most of Australia) all the others are easy pickings!
So see?.. this is yet another reason why you located your APO down under :thumbsup:
08-05-2012, 09:30 PM
Not only is N6752 the third brightest globular, it is also one of the nearest! According to the Globular Cluster Catalog of W.E. Harris, it is at 4 kiloparsecs, in other words.....13,000 light years.
This relatively small (for a globular!) distance is one reason why this is one of the few globulars in which stars can easily be seen when visually observing with a 3 inch telescope.
But M22 is even nearer (3.2 kiloparsecs).....that's why it is so gigantic, in angular diameter.
cheers, mad galaxy man
09-05-2012, 02:30 AM
The Starfish is one of my favourite naked eye globs, and is a worthy imaging target as well, as you have shown.
09-05-2012, 01:09 PM
Nice photo. I like the star colour and clarity. Looks to me like the background could be blacker, but it's OK.
Interesting info coming up in the thread too.
09-05-2012, 01:59 PM
Thanks Mike! Well, I never end to learn new things, this is one of the great points of this passion :P
Haha, indeed, now I have another good argument supporting my observatory down under, next time my wife is complaining about the cost :D
Thanks again for your informative reply :thumbsup:
09-05-2012, 03:34 PM
Here is The Catalog of Milky Way Globular clusters, by Bill Harris (W.E. Harris). It should be about as up to date as any catalog of globulars can be, because Harris has spent his entire life researching globular star clusters.
There are some very exciting & gripping & interesting numbers here. This catalog reads like a thriller!!
(("Notepad" in Windows, mucks up the formatting of this text file, but any of the millions of text file readers available on the internet will display this file properly.
"WordPad" will probably work. ))
14-05-2012, 09:13 AM
Thanks a lot Rick, yeah I very much enjoy having the wire spider.
Thank you Steve :)
Thanks Trevor :)
Thank you Brendan, do you mean they should be more red rather than orange, or that the whole cluster should be more white as globulars are traditionally presented?
Thanks Greg, yes I tried to show the actual colours of this globular.
Thank you, yes the colours are the main feature of globulars I think, but it's not often brought out in the processing.
Thanks Craig :) It's probably a matter of taste, most globular images show them quite white, where in reality they are reddish. I tried to bring out the latter here.
Thank you Grant :) Yes 24:8:8:8 is the total. Each L frame was 90 seconds and RGB was 60 seconds each. I would have gone longer but the Moon light prevented this.
Thank you Mike - I had to image something while I wait for the Moon to disappear ;) But they turned out quite nice indeed!
Thanks Lester, glad you liked it :)
Thank you for your kind words Mike :)
Thank you Marco, Mike beat me to the ranking :P
I find that, apart from limiting magnitude, the challenge on moonlit nights is mainly the gradients. In some directions I get quite strong flares and stray light from the Moon, so I'm limited in what I can image when the Moon is up. Of course it doesn't help that I use a truss tube scope - I should paobably make a shroud some day.
Thanks a lot Paul, glad you liked it :)
Hehe thanks for the info Mike, always good to be reminded of how spoiled we are down this way :lol::P
Thanks for the details Robert. I thought M4 was the nearest, at some 7500 light years?
Thank you Ric, yes visually it's very impressive too!
Thank you Roger. I think you are right about the background, I'll have a look again.
Thanks for that Robert, that's a great list for us globular aficionados :) I'll look forward to tracking down some of the more challenging ones there.
vBulletin® v3.8.7, Copyright ©2000-2013, vBulletin Solutions, Inc.