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FirstSight
Carpal Tunnel
Reged: 12/26/05
Posts: 2512
Loc: Raleigh, NC
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Two nights ago, I easily located globular cluster M53 on a line about a third of the way along a direct line from Arcturus to Deneb (rearmost star in Leo). It's not quite so large, bright, nor easily resolved into individual stars at a given magnification as M3 or M13, but an obvious gem in any of my eyepieces.
According to charts, a half degree or less southward of M53 lies another smaller globular cluster, NGC 5053, which is listed as having just over 60% the diameter of M53 and about two levels dimmer magnitude (9.8 v. 7.7) and surface brightness (12 v. 14.29). Yet try as I might to carefully scan the appropriate area around M53, I could detect nothing resembling another globular cluster.
Sky conditions were quite good - in fact, good enough that I was able to find M101 only about 15 minutes later (M101 is listed as magnitude 7.9, but more importantly, as having over half a magnitude lower surface brightness than NGC 5053 (14.90 for M101, 14.29 for NGC 5053). Skies were mainly clear, with very good seeing and transparency and mag 5.5 sky in the overhead region of observation.
My observation of M53/attempt at NGC 5053 was probably an hour before moonrise, continuing over a 15 min-period, and of M101 probably a half-hour before moonrise, just as Jupiter was starting to become prominent in the southeast, but while it was still well too low for good viewing.
Any ideas why I might have been unable to find/see NGC5053, or suggestions for finding/seeing dimmer globulars such as this? I find it ironic that I could find such a comparatively difficult galactic object as M101, but not a modestly brighter, albeit small, globular cluster (I know; M101 may be a piece of cake for some of you in certain parts of Arizona or New Mexico, but too many of us live in mud pie country as far as M101 is concerned).
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Chris M., aka "First Sight"
Orion XT12i Dob with Moonlite CR-2 focuser
WO Megrez 90 refractor on UniStar Light mount
Nikon 10x50 Binoculars
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 6757
Loc: Beatrice, Nebraska
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NGC 5053 is a somewhat sparse globular with very faint component stars (the brightest are around magnitude 13.8, with the horizontal branch sitting way down at 16.7) It is somewhat smaller than nearby M53 and does not have the kind of highly concentrated central glow that many globular show. This gives it a pretty low surface brightness, so it can be a lot tougher than it looks. That having been said, I have managed to at least glimse its faint glow in a little 80mm f/5 "short tube" refractor at about 40x, but it was difficult in that aperture. I first found NGC 5053 many years ago in my 8 inch f/7 Newtonian using about 53x, but again, it is pretty faint and rather diffuse looking so it can be easy to overlook. In my 10 inch f/5.6 Newtonian on a good dark-sky May evening in 2002, NGC 5053 appeared as a good-sized but rather faint diffuse fuzzy patch with a *very* slight brightening towards its middle at 59x. However, at 101x, a large number of *very* faint stars became visible, with some coming and going with the seeing. 178x revealed a few more stars (perhaps as many as 50 in total), but not a lot more than had been seen at 101x. At 178x, the globular looked a bit like a rather rich but very faint circular open cluster with only a slight concentration of stars towards its middle. Get to a dark sky site (ZLM 5.8 or fainter), look for something near the limits of your vision, use something between 40x and 80x, and keep trying. Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
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SaberScorpX
Post Laureate
Reged: 01/12/05
Posts: 4120
Loc: illinois, usa
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5053 is a Herschel II target, so we're talking transparent 6th mag skies,
plenty of dark adaptation, and possibly averted vision for initial detection.
A much dimmer and diffuse globular than m53, look for a dusty, very loose
'open cluster' appearance.
My 8" will reveal 5053 as a fairly large, mostly unresolved glow just less
than a degree SE of m53. A 9.5mag sun lies just off its eastern border.
NGC/IC Data
Stephen Saber
PAC/Astronomical League
http://www.geocities.com/saberscorpx/home.html
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amirab
super member
Reged: 03/03/04
Posts: 193
Loc: Israel
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Hi.
NGC 5053 is a tough target especialy since it"s easy to locate but once you on the spot you can"t see it .
I spend houres to try and see it .
eventualy I saw it using a 15 dob in a mag 6 sky. It is certainly not a regular glob. very dim and sparse.
Amir
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Amir
AT-111 APO TRIPLET
TV Genesis- SDF
MEADE LX90 8' UHTC
MEADE STARFINDER 12.5' DOB.
APOGEE SA-88-RA BINO.
OBERWERK ULTRA 15X70
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MikeRatcliff
Pooh-Bah
Reged: 06/12/04
Posts: 1105
Loc: Redlands, CA
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5053 is listed as a "challenge object" in the Canadian RASC handbook.
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16" f/4.9 dob
Tele Vue Plossls 32,25,20,15,11
13 Nagler T6
10.5 Pentax XL
Brandon 32, 16
12.5 UO ortho, 9 Circle T ortho
2x TV Barlow
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Jim Nelson
professor emeritus
Reged: 05/10/05
Posts: 718
Loc: Hanover, New Hampshire
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I've found 5053, but it was such a phantom in my 6inch scope that I had to sketch its position in the starfield to double-check later. (turns out I did have it!). This was from pretty good (prob mag 5.8 or so? I don't have my records handy) skies.
<<(M101 is listed as magnitude 7.9, but more importantly, as having over half a magnitude lower surface brightness than NGC 5053 (14.90 for M101, 14.29 for NGC 5053). >>
Yep! There's no single number that tells you how difficult an object is, is there? Total brightness, surface brightness, and size all interact in interesting and endlessly frustrating ways! 5053, while having a slightly higher surface brightness, is still smaller and less bright overall. In this case, it loses out. M101 is a much easier object than NGC5053 in my experience.
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Orion XT6
Orion Starblast
Swift 8x42 Ultra Lite
Edited by Jim Nelson (04/19/06 09:43 AM)
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MichaelH
member
Reged: 10/09/05
Posts: 82
Loc: Ontario, Canada
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I unsuccessfully tried to see NGC 5053 with an 8" from moderate skies some years ago. It is definitely not an easy golbular to spot.
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Michael and Louise
Astronomical Sketches web-site
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 6757
Loc: Beatrice, Nebraska
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Quote:
I've found 5053, but it was such a phantom in my 6inch scope that I had to sketch its position in the starfield to double-check later. (turns out I did have it!). This was from pretty good (prob mag 5.8 or so? I don't have my records handy) skies.
<<(M101 is listed as magnitude 7.9, but more importantly, as having over half a magnitude lower surface brightness than NGC 5053 (14.90 for M101, 14.29 for NGC 5053). >>
Yep! There's no single number that tells you how difficult an object is, is there? Total brightness, surface brightness, and size all interact in interesting and endlessly frustrating ways! 5053, while having a slightly higher surface brightness, is still smaller and less bright overall. In this case, it loses out. M101 is a much easier object than NGC5053 in my experience.
Well, with globular clusters there are a few numbers which people need to be aware of. Other than the total magnitude and angular size, the first significant number (if you are interested in actually seeing stars) is the "giant tip" magnitude, which is generally the brightness of the very brightest stars in the cluster. The second is the "horizontal branch" magnitude, which is the brightness of stars on the so-called "horizontal branch" of the H-R diagram (color index vs. magnitude) which gives a sort of brightness level where you might see a moderate number of the cluster's brighter component stars. For example, M13's brightest star is about magnitude 11.9, which means that a good 3 inch telescope at high power under excellent conditions might start to show just a few stars around the edges of the cluster. However, the horizontal branch magnitude is about 15th magnitude, so a 3 inch generally makes M13 appear as a big fuzzy ball with a brighter core and a hint of granularity around the edges with only a very few discreet stars visible. However a 10 inch can easily reach that 15th magnitude Horizontal Branch level, so the cluster is spectacular at high power in such an aperture. Indeed, I did some extended star counts in sectors of M13 and came up with an estimate of between 1200 to perhaps 1700 stars being visible in a 10 inch. Another example is M22, where the giant tip magnitude is 10.7 and the horizontal branch is at 14.2, so that cluster shows a number of stars even in a 2.4 inch refractor and is actually a somewhat better object for resolution in small to moderate aperture telescopes than M13 is. Both the V(tip) and V(HB) magnitudes are provided by the Field Guide to Uranometria as well as in some software programs like MEGASTAR, so these numbers can help you get an idea of what you may see when you hunt down these distant clusters. Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
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btschumy
Think Astronomy
Reged: 04/13/04
Posts: 1107
Loc: Austin, TX, USA
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Here is a screenshot showing where the two globulars are located in our galaxy:
M53 and NGC 5053. As you can see, they are both physically close to one another with 5053 being slightly closer. Looking at their luminosity data, you can see that 5053 is only about 1/9 as luminous as M53. It is also only 3/4 of its size. No wonder it is so hard to see.
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Bill Tschumy
Where is M13? Freeware -- Add a new dimension to your observing.
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10420
Loc: Amargosa Valley, NV, USA
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Interesting site, Bill!
I saw NGC 5053 for the first time last night with my 10" dob. It was NOT easy. I wasn't really sure what to look for, and assuming simply a smaller, fainter version of M53 I searched all around the field without success. Part of the reason it's so difficult is that there is a brighter star near one edge that tends to overpower it. Nevertheless, at high power I could just barely resolve a very few individual stars, and detect the faint background glow.
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"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
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RRaubach
AstroCowboy
Reged: 01/26/05
Posts: 2173
Loc: Douglas (Converse County),WY
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FWIW--
NGC 5053 has bedeviled many amateurs, thinking that it should be pretty easy based on the listed magnitude. It is a Class XII globular on the Shapley-Sawyer scale, which means it is very "loose" in structure; it is also pretty large in diameter relative to brightness, hence a very low surface brightness object. This makes it a good target only under the darkest of skies, and is a great object on which to practice your averted vision!
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Rodger
Meade SN-10 (UHTC) on Tak EM-200 mount/Antares rotating rings. Moonlite focuser.
Parallax 14.5" Newtonian on HD 200 mount (arriving soon!) w/ conical Royce mirror.
TMB 203 f/7 APO refractor on Tak NJP-160 mount.
Discovery 12.5" PDHQ
Schneider 18x80 "Flakfernrohr" binoculars/tripod mounted. Canon 15x50 IS binoculars
Unihedron Sky Quality Meter
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FirstSight
Carpal Tunnel
Reged: 12/26/05
Posts: 2512
Loc: Raleigh, NC
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Thanks for all the knowledgeable, experienced feedback everyone! I don't feel quite so blind and dumb now.
The concepts of "sparse" and "globular cluster" don't play together well in my mind. However, your comments remind me that we're actually dealing with from a terrestrial-bound perspective is our available *view* of such objects, i.e. how many stars are bright enough to be individually or collectively seen through amateur scopes, and not their true nature, which is how many stars are actually in the cluster. Usually with globular clusters, our view corresponds well with presenting their true nature, but NGC 5053 is a reminder that t'aint necessarily so with dimmer clusters.
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Chris M., aka "First Sight"
Orion XT12i Dob with Moonlite CR-2 focuser
WO Megrez 90 refractor on UniStar Light mount
Nikon 10x50 Binoculars
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btschumy
Think Astronomy
Reged: 04/13/04
Posts: 1107
Loc: Austin, TX, USA
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As you say, globular clusters are not necessarily tight balls of many stars. The more pertinent characteristics of a globular are that it's composed of older, Population 2 stars and it location in the galactic halo. There are numerous globulars that don't look like globulars.
Some of the Terzan globular clusters only have luminosities in the range of 5 to 10 Suns and their physical size may only be 1 or 2 light-years across.
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Bill Tschumy
Where is M13? Freeware -- Add a new dimension to your observing.
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RRaubach
AstroCowboy
Reged: 01/26/05
Posts: 2173
Loc: Douglas (Converse County),WY
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I was under the impression that most of the Terzan globulars are heavily obscured and are not extreme halo objects, but are near the galactic center? Most of the Terzans are in Scorpius and Sagittarius.
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Rodger
Meade SN-10 (UHTC) on Tak EM-200 mount/Antares rotating rings. Moonlite focuser.
Parallax 14.5" Newtonian on HD 200 mount (arriving soon!) w/ conical Royce mirror.
TMB 203 f/7 APO refractor on Tak NJP-160 mount.
Discovery 12.5" PDHQ
Schneider 18x80 "Flakfernrohr" binoculars/tripod mounted. Canon 15x50 IS binoculars
Unihedron Sky Quality Meter
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btschumy
Think Astronomy
Reged: 04/13/04
Posts: 1107
Loc: Austin, TX, USA
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Rodger,
You are right that the Terzan globs tend to be in the galactic plane although 4 of them are indeed halo objects. Terzan 6 is located in the Sagittarius arm only about 4800 light-years away. It does not appear to be undergoing extreme extinction. Terzan 2 is similarly located. I think these are just very small and sparse globulars.
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Bill Tschumy
Where is M13? Freeware -- Add a new dimension to your observing.
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10420
Loc: Amargosa Valley, NV, USA
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Quote:
As you say, globular clusters are not necessarily tight balls of many stars. The more pertinent characteristics of a globular are that it's composed of older, Population 2 stars and it location in the galactic halo. There are numerous globulars that don't look like globulars.
Although in some other galaxies there are young-looking globulars that would (presumably) have formed from more metal-rich stars.
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"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
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btschumy
Think Astronomy
Reged: 04/13/04
Posts: 1107
Loc: Austin, TX, USA
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Quote:
Although in some other galaxies there are young-looking globulars that would (presumably) have formed from more metal-rich stars.
True, there are a small number of globs (particularly in other galaxies) that appear to be younger and may have more metals. Since we don't really understand how globulars formed, it's not clear what these are or how they got there.
So maybe I should waffle a bit on my statement that low metallicity is a defining characteristic of globulars. Thanks for pointing that out.
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Bill Tschumy
Where is M13? Freeware -- Add a new dimension to your observing.
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