1/7/11 Through an unexpected gap in the clouds

[Paddy]

I'd given up on observing on Friday night, went out to get some firewood before going to bed and behold! the sky was ablaze with stars. Moreover there were distinct dark bits as well - the clearest night I've seen for a long time. So out came the scope. And I got my tape recorder working again.

So I played for a while with some GCs, found a very intriguing PN and enjoyed some open clusters.

Here are the notes. Sorry, the resurrection of the recorder has probably increased the verbiage. Thanks for reading.

Telescope 410mm (16”) f4.9 tri-dob reflector
Eyepieces 28mm UWAN, 17,13,9 mm Naglers, Paracorr
Navigation: Night Sky Observer’s Guide (NSOG), Uranometria Vol 2
Data from SEDS list of galactic GCs and the NGC/IC project

http://seds.org/messier/xtra/supp/mw_gc.html
http://www.ngcicproject.org/pubdb.htm

No plan as I was not expecting to see the sky, but galactic centre and GCs beckon.

2300

Seeing good 2/5. Transparency the best I’ve seen for many months. The Pipe nebula is very crisp and dark

NGC 5946 GC in Norma Class IX
15:35:28.52 -50:39:34.8
Vmag9.61 Dia 3.0’

175X Nicely concentrated GC, reasonably bright with obvious core. The halo beyond the core is quite large and soft. Looks about 4’ dia. and the core is about 1’. No stars resolved but the GC has a grainy texture. Good contrast in spite of being in a very busy star field. A foreground star is apparent within the southern edge of the halo.

http://spider.seds.org/ngc/ngcdss.cgi?obj=NGC!5946&r=15:35.5&d=-50:40&e=J2000&h=15&w=15&f=GIF&c=none
(http://spider.seds.org/ngc/ngcdss.cgi?obj=NGC%215946&r=15:35.5&d=-50:40&e=J2000&h=15&w=15&f=GIF&c=none)
NGC 6356 GC in Ophiuchus Class II
17:23:34.93 -17:48:46.
Vmag 8.25 Dia. 10.0

175X A lovely soft glow, quite large and well concentrated with soft core fading into the halo. Very regularly round the outer halo looks about 7’ across, with the core about 2’ with the impression of a sharp point of light at the core. No stars resolved, but quite grainy.

http://spider.seds.org/ngc/ngc.cgi?6356

NGC 6333/Messier 9 GC in Ophiuchus Class VIII
17:19:11.26 -18:30:57.
Vmag 7.72 Dia 12.0

175X Not much bigger than nearby NGC 6333, but significantly brighter and much less concentrated. There are 20-30 resolvable stars. It is hard to tell whether the GC is irregular or if the irregular appearance is due to the plethora of objects around it. No distinct core. There is a wide splash of luminance off the northern edge. Looks about 8’ across.

http://spider.seds.org/ngc/ngc.cgi?6333

NGC 6342 GC in Ophiuchus Class IV
17:21:10.08 -19:35:14.
Vmag 9.66 Dia. 4.4

175X This GC sits on the edge of dark nebula Barnard 259. A small glow in the night sky with quite a marked core amongst many background stars. No stars resolved, mostly quite regular looks about 4’ across.

http://spider.seds.org/ngc/ngcdss.cgi?obj=NGC!6342&r=17:21.2&d=-19:35&e=J2000&h=15&w=15&f=GIF&c=none (http://spider.seds.org/ngc/ngcdss.cgi?obj=NGC%216342&r=17:21.2&d=-19:35&e=J2000&h=15&w=15&f=GIF&c=none)

NGC 6440 GC in Sagittarius Class V
17:48:52.70 -20:21:36.
Vmag 9.20 Dia. 4.4

175X Looks very similar to nearby 6342. Quite concentrated distinct soft glow in the midst of a line of f/ground stars. A marked core fading gently to a soft halo. No stars resolved.

http://spider.seds.org/ngc/ngc.cgi?6440
(http://spider.seds.org/ngc/ngc.cgi?6440)
NGC 6445 PN in Sagittarius Class 3b(3)
17h 49m 15.0s -20º 00' 34"
Vmag. 11 2.8’x 0.9’

250X This is quite a large PN and it’s hard to tell at first whether it is a ring or two parallel lines. As I keep observing it appears more like a thick-walled, box-shaped ring, but the ring is fainter on the western edge as well as somewhat fainter on the eastern edge. The ring appears to have tiny bright knots so that it looks a bit sparkly. No central star is seen. Brightens with UHC filter, which confirms that it is a ring. Moreover there is a tongue of fainter light protruding from the western soft edge of the ring which looks even more sparky. There also appears to be a soft central glow, surrounded by a dark annulus within the outer bright ring. OIII confirms the above obs, the inner section brightening further and the sparkles in the ring intensifying. The western edge looks quite disrupted.

http://spider.seds.org/ngc/ngcdss.cgi?obj=NGC!6445&r=17:49.2&d=-20:01&e=J2000&h=15&w=15&f=GIF&c=none (http://spider.seds.org/ngc/ngcdss.cgi?obj=NGC%216445&r=17:49.2&d=-20:01&e=J2000&h=15&w=15&f=GIF&c=none)

NGC 6494/Messier 23 OC in Sagittarius Class II 2 r
17h 57m 04.7s -18º 59' 07"
Vmag 5.5 Dia 30’

90X A splendid OC looks about 30’x50’. Most members look similar magnitude and similar colour. A delicate line of stars trails to the north towards a bright star which I suspect is not a member of the OC. Behind it all is the mottled glow of countless disc stars.

http://spider.seds.org/ngc/ngc.cgi?6494

NGC 6531/Messier 21 OC in Sagittarius Class I 3 r
18h 04m 13.4s -22º 29' 24"
Vmag 5.9 Dia 15’

135X This is a stunning cluster next to the Trifid nebula with an intriguing asterism which looks like an angular P-shape (E-W) joined to an elegant loop off about 10 stars to the north. This asterism looks about 6’x6’. There is some variety in the magnitude of the stars, but not much variation in colour. It stands out quite well in the field.

http://spider.seds.org/ngc/ngcdss.cgi?obj=NGC!6531!=!M21&r=18:04.6&d=-22:30&e=J2000&h=15.6&w=15.6&f=GIF&c=none (http://spider.seds.org/ngc/ngcdss.cgi?obj=NGC%216531%21=%21M21&r=18:04.6&d=-22:30&e=J2000&h=15.6&w=15.6&f=GIF&c=none)

Bands of thin high cloud start to move in - I watch the Pipe nebula go from stunning to rubbish and so the session endeth.

[pgc hunter]

Skies clearing unexpectedly :eyepop: gotta just love that :D
Interesting write up once again Paddy. Sometimes it's refreshing to just roll out the scope without having a plan and lists to follow.

How did you go with the seeing? Interested as I was out on the Saturday morning trying observe Jupiter (2/7) and I can safely say it was the WORST seeing I've ever seen in my life ('scuse the pun). Could just barely see HINTS of the two main belts with an 8" scope :rolleyes:

[Paddy]

The seeing was quite good up up here. I could manage 250X for the PN with no trouble. Perhaps the Great Divide divides seeing as well.

[ngcles]

Hi Paddy & All,

Very interesting report and thank you for taking the time to share it with us. M9, like many other G.Cs in Ophiuchus has a fairly conspicuous dark nebula (Barnard 64) nearby to the W and SW that is an interesting contrast. Here is how I saw M9 back 6 years ago with 46cm from Mudgee:

M 9 NGC 6333 Globular Cluster
*RA: 17h 19m 11.8s Dec: -18° 30' 59"
Mag: 7.8 Mag V(tip): 13.5 Mag V(HB): 16.2B-V (tip): ---
Size: 12.0'

LDN 173Dark Nebula
RA: 17h 17m 19.2s Dec: -18° 31' 03"
Mag: ---Size: 12.0'x8.0' Class:

x185 27' TF

One of the lesser Messier clusters in Ophiuchus, but none the less a splendid object which is well resolved. Seems to have lower CC -- perhaps 8-9 with a broad moderate concentration of stars toward the centre. It is partially to well resolved at x185 with perhaps over 100 mag 13 to threshold stars peppered over the face of the cluster which has a hazy granular background. Appears perhaps 9' diameter. The two brightest resolved stars are 1/2 way out on the S side of the halo and in an apparent pair with a clump of fainter stars surrounding them. Overall seems round. There is a conspicuous large void of stars to the W and SW of the cluster which shows up better with low power -- this is B 64 or LDN 173.B 64. Appears 20' to the W and SW as an irregular shaped large 15' x 15' void with almost no faint stars within it.


Best,

Les D

[Paddy]

Thanks Les. Love your description - inspires me to go back and have another look.

[kustard]

Do you often swap out EP's when observing just to see if you can zoom in/out for a different perspective or is it a case of a certain mag being the best for the objects you are looking at?

Those are some fine observations as always :)

[Paddy]

Thanks Simon. I do swap eyepieces quite a bit, but lately I've only tended to record obs at one magnification that seems the best. I do usually end up with 175X for most GCs, 175-250 for galaxies and 250X for PNs (higher if seeing allows) and mags for OC depend on the size.

[michaellxv]

Lovely descriptions Paddy. You seem to be very systematic in the features you describe. Do you have a specific routine or list of features that you look for?

[Paddy]

Thanks Michael. I do have a sort of system, some of which is loosely based on the way the objects are classified. I can't remember all the classes when observing, but for example, the Trumpler system for open clusters includes how well detached the cluster is from the surrounds, the variation in magnitude and how many stars are involved. Similarly the GC system is about concentration. But the patterns of stars that I see are some of the most beautiful things to me even the little ones around globulars, so I try to describe them if they're not too complex. PNs and galaxies I just try to get as many details down as I can.

[michaellxv]

I should go do some reading on how different objects get classified then. This would no doubt help the viewing experience also.

[orestis]

Great stuff Paddy:thumbsup:,

Regards Orestis:)

[Paddy]

Thanks Orestis.

[astrospotter]

Fun read Paddy!

Globs to me are up there as nice targets that hold my interest. Your report is very timely in my own quest that started at a 4 day huge star party way up north here. As always I enjoy your reports as they hold lots of goodies and often ones I cannot see up north at +36 degrees.

If and only if you like globs need you read farther ...

What intrigues me about the globulars is the concentration class. They were all rated with DSS plates and so on but visually it is not so easy to squeeze 12 classes of concentration for these GCs for various reasons specific to visual observing. Generally we can say low/medium/high and MAYBE up to 5 classes like that very fine low concentration glob in Musca (N4372 I believe, and I really like that one). We are all tricked visually as we can NEVER see where a glob actually ends. I always judge WAY too small knowing full well that will be the case.

It is even with my 18" dob generally almost impossible to judge the very limits of a glob because the glow fades to nothing. So for concentration class which is required for the next Astronomical League club I am working on I decided to try other ways to visually judge them as I re-observe 50 or more for this club. I am sure I will not get the values right and prior to this I generally rated 'low', medium, high or in cases such as that very low concentrated one in Musca 'very low'.

At the star party in 1st week of July I covered 22 globs (among other things) and decided to try to note things using this method and then judge these numbers using stated GC total size and see if I can find a connection to concentration class they are rated at in books.

Here is the plan:
1) Use 9mmNag, 216x, and judge outer limits of the glow. Also discuss a 'guess' at class and then note any distinct features such as 'streamers'.
2) Use 3.5mmNag, 555x (yes it's close to insane but I am judging glow now and not so much resolution). For this I try to estimate 'covered core' which is where there is full coverage with no dark non-star gaps. I use 3.5mm to get better diameter measurement but seeing was really nice so I felt it was ok for this measurement.
3) Also with 3.5mm 555x measure 'mid-glob boundry' which is where you can say for sure you are about at 50% star coverage with lots of dark spots and stars about 50/50.

I hope to try to correlate this to real measurements but I have little faith.

Thanks for the real interesting read on the south globs I cannot see well from up here Paddy. I always enjoy your ORs, nicely done.

Mark (from the North)

[Paddy]

Thanks Mark for you feedback and for a very interesting read. Your comments about assessing the class of GCs visually rings very true - I reckon 3-5 classes is about the best that can be done. And it is as you say so hard to find the boundary of the cluster - I am often amazed at how poor my visual estimates of the size of GCs is vs what is in the books. I like the sound of your system. I look forward very much to hearing how you go.