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NGC 6441 (14,733 of 18,816)

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NGC 6441

NGC 6441, Dunlop 557, C 1746-370, Cl VDBH 248, GCl 78, Bennett 99, h 3705, GC 4332

RA: 17h 50m 12.84s
Dec: −37° 03′ 3.9″

Con: Scorpius
Ch: MSA:1437, U2:377, SA:22

Ref: SIMBAD, Archinal&Hynes (2003), SEDS

(reference key)

Type: globular cluster

Mag: B=9.26, V=8

Size: 9.6′
PA: ?

Historical observations

Dunlop, James (1827)

James Dunlop discovered this object from Paramatta, New South Wales, and included it as No. 557 in his catalogue of 1827. Using a 9-inch f/12 telescope, he described it as "a small well-defined rather bright nebula, about 20 arcseconds diameter, a very small star precedes it, but it is not involved; following gamma Telescopii."

John Herschel (1847) Cape Observations

Observed by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "globular, B, R, vgbM, up to a blaze. In field with Gamma Telescopii, and nearly on the same parallel; with left eye I barely see it resolved into stars 18 or 20m. The whole ground of the heavens, for an immense extent, is thickly sown with such stars. A beautiful object." On a second occassion he called it "globular, B, R, 1.5', vgbM, resolvable (barely so), a very regularly graduating neb or cluster; in field with gamma Telescopii."

Published comments

Melotte, P.J. (1915)

A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.

Doig, P. (1925)

Journal BAA, 36(3), Dec, p91

about 1.5' diam.

Sulentic & Tifft (1973)

The RNGC (Sulentic and Tifft 1973) notes that this is a 9.0 mag globular cluster.

Bailey, S.I. (1908)

"globular cluster, extremely condensed"

Bailey, S.I. (1908) A catalogue of bright stars and nebulae. Ann.Harv.Coll.Obs., 60(8), 199.

Harris, W.E. (1997)

RA 17 50 12.9 (2000) Dec -37 03 04 Integrated V magnitude 7.15 Central surface brightness, V magnitudes per square arcsecond 14.99 Integrated spectral type G2 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 1.85 Core radius in arcmin .11. ["Catalog Of Parameters For Milky Way Globular Clusters", compiled by William E. Harris, McMaster University. (Revised: May 15, 1997; from http://www.physics.mcmaster.ca/Globular.html; Harris, W.E. 1996, AJ, 112, 1487) ]

Modern observations

Tom Lorenzin

Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "8M; 3' diameter; bright, round and compressed; unresolved at 200X; bright star in foreground; 3.5M G SCO in same field a few minutes W."

Lim, Derrick (IAAC)

Observer: Derrick Lim

Your skills: Intermediate (some years)

Date/time of observation: 1:30am Arizona Time (GMT -7)

Location of site: Tempe, AZ (Lat 33h24m54s, Elev ??)

Site classification: Suburban

Sky darkness: 4.5 Limiting magnitude

Seeing: 7 1-10 Seeing Scale (10 best)

Moon presence: Major - gibbous or near object

Instrument: 6" f/5

Magnification: 38X and 75X

Filter(s): none

This cluster is located right next to the bright star G scorpii. My first impression of this cluster when I saw it with 38X magnification is "Wow! It's really bright!!". I could see it clearly without using averted vision. At 75X It appears even brighter. I tried to see whether the cluster was resolved at this power, but the moon was too bright. However, I did notice some condensation in this globular. I also noticed a star (about 9th or 10th magnitude??) to the SW.

[amastro] JaFu2

Dear DS fans,

On Sun, 4 Jul 1999, Tom Polakis wrote:

] there is a 0.5% probability of it being a chance alignment. They are even

] more certain about the location in a globular of JaFu 2, which is found in

] NGC 6441. The paper is AJ 114,2611 (12/97), which is available on-line in

] I was unable to find any measurements of the brightness of either planetary

] in the paper, but neither one of them looked particularly faint on the

] image. Both objects are in globular country, at about 18h R.A., which

] means they're currently on the meridian at a convenient hour. Who will be

] the first to spot them?

Thanks to the finders provided by Tom Polakis, I think I spotted JaFu2 with

the 1m, f/16 scope of Sutherland Observatory, South Africa, using 350x

magnification. The nearby bright star is quite disturbing. Here is an ASCII

kind of drawing, N is up, E is to the left.

#GC

*c

*e *b

*PL *d

*a

GC denotes the glob's core, "a" is quite a bright star, "b,c,d" are readily

visible, "e" is a bit diffuse because it consists of several faint stars,

the PL is quite difficult, just visible with averted vision, sometimes

merging with "e". It can't be brighter than V=16. Seeing conditions are not

the best, and I had only a few minutes, because bulge has risen and I am

observing microlensing events...

Best regards,

Gaspar

******************************** *

Gaspar A. Bakos

Currently at Sutherland Observatory, South Africa

Konkoly Observatory, Budapest, Hungary

bakos@cs.elte.hu (forwarded to bakos@stsci.edu)

bakos@stsci.edu (forwarded to planet@dandipc.saao.ac.za)

Safety mail: bakos@konkoly.hu

******************************** *

Steve Coe

Steve Coe, observing with a 17.5" f/4.5 at 100X, notes: "Bright, pretty large, round, very bright middle, very grainy at 165X. Two stars are resolved at 320X. Seen in the finder.

Ed Finlay

1993 May 30

Ed Finlay, observing with a Meade 4-inch ED APO refractor from Johannesburg, 1993 May 30, notes "globular cluster east of G Scorpii. Easy to find, barely visible whitish patch size 3'. At 102x can see faint star at one edge. Remarkable what you can see when one's eyes are dark adapted!"

Contemporary observations

Gabriel Giust

1994 April 10

"Bright! Details are not observed because of the proximity to G Sco. Seen in a wide field ocular (40mm)." Gabriel Giust, 1994 April 10, 8-inch f/6.7 reflector, 9.7mm Super Plossl, San Isidro, Buenos Aires.

Auke Slotegraaf

1995

Observing with a 6-inch f/8.6 Newtonian this globular is quite easily shown at 52x. The cluster appears as a ghostly after-image of the orange star G Sco, which it follows. There is a 10m star to the SW of the cluster 3.5 times closer than G Sco. The cluster appears nebulous, round, bM, pL, pB with a broad centre. The combination cluster-G Sco makes a very attractive sight. It should be quite a challenge in binoculars.

1997 July 9

1997 July 9, Wednesday, 20:00 - 22:00 Jonkershoek. 11x80's tripod-mounted. Moderate conditions. Despite being near the bright G Sco, averted vision clearly shows this neat, small globular cluster.

Magda Streicher

1997 August 05

Location: Pietersburg South 23 53. East 29 28.

Sky conditions: Fair.

Instrument: Meade 12 inch.( Eyepiece super 40mm).

Date: 1997 August 05

Field of view: 52.7 minutes.

A bright medium sized globular cluster with definite mottled edges. Brighter towards the middle in a fairly busy starfield. Towards the south-west a very very bright yellow orange star visible. Pinpoint stars are scattered in the field of view.

(no date)

12-inch f/10 SCT (EP: 2-inch 40mm SW 76x 53' fov; 2-inch 32mm SW 95x 42' fov; 2-inch 14mm UW 218x 23' fov)

Situated just 3'.1 arc minute east of yellow G Scorpii. An easy bright, medium sized globular cluster with definite mottled edges. It sport a bright outstanding core. A faint 10th magnitude star can be seen embedded in the south western part. James Dunlop discovered this object from Paramatta, New South Wales and included it in his catalogue of the year 1827. The planetary nebula PK353.5-04.9 seems to be just to the west of G Scorpii. With G Scorpii fairly bright I think this is almost impossible to observe. (Mag 7.2; size 9.6'; brightest stars 15.4 mag. )

Chris Vermeulen

2007 November 09

2007-11-9

West Village, Krugersdorp

6" Dobsonian

Clear Skies, Very good seeing conditions, No Moon

Light pollution: Low - Surrounding houselights in area and city lights reflect an amber glow on the horizon, mainly to the West, but no direct influence on observation.

A rather feint fuzzy double object detected at Scorpio's tail just below G Scorpii at the tip of Scorpio's tail. At first it appeared as a very feint nebula ("A") with a small companion ("B") just above and to the right. Through 25 mm eyepiece (48x magnification) it was relatively easy to spot, however it is not detectable through the finder scope. The best way to find this object is to locate G Scorpii, a yellow-orange star right at the tip of Scorpio's tail (see sketch below) in the finder scope, and then with a low magnification eyepiece focus on G Scorpii. Both "A" and "B" will appear just below G Scorpii as 2 fuzzy objects in the field of view.

Through the finder scope the surrounding area is quite impressive as one can even see M7 in view. With a low magnification (25 mm eyepiece) the field of view is narrowed down considerably, but still offers a magnificent view with several bright and feint stars visible. Most notable is G Scorpii, a yellow-orange coloured star that stands out far above the other stars in the field of view. Going onto higher magnification, 10 mm eyepiece and 10 mm eyepiece with 2x Barlow lens respectively, does not do the surrounding area any justice as the field of view is very small. However the most prominent star still remains G Scorpii. With the 10 mm eyepiece about 7 other very feint stars could be counted, excluding G Scorpii and "B", which could no quite be said with certainty if it was a very feint star or object.

"A" appeared about 4x the size of "B". With a 10 mm eyepiece (120x magnification) more detail became apparent, although both "A" and "B" had a fuzzy appearance like feint globular clusters. With the addition of a 2x Barlow Lens together with the 10 mm eyepiece (240x magnification) "B" could now be clearly distinguished from "A". "B" appeared to be a very feint star, but still it seemed as if there was some cloudiness surrounding it, therefore it cannot be said with certainty that it is a star or another object. "A" could now be clearly distinguished and appeared more like a globular cluster with a compact centre and a general grainy appearance of globular clusters at high magnification, but was not verified at the time.

Observation conditions were very favourable, despite the lights of the neighbouring houses and city lights. The sky was clear with no clouds visible and no Moon. There was still a very feint afterglow of the Sun that set, but it had no effect on the observation, as the object was well clear of this afterglow. The description and sketch was made with ease due to the high visibility of G Scorpii that was used as a marker to spot the object. At first it was uncertain as to what the object was, even though through high magnification it appeared to be a globular cluster. This was verified with the Cartes du Ciel database that it was in fact a globular cluster (NGC6441). However its companion ("B") could not be located on this database and still remains unknown. Observation after 20h30 became rather difficult as it was situated to the West and Scorpio was setting behind the high treetops.

Richard Ford

2016, June, 4th

Location:Perdeberg.

Time:7:50pm.

Sky Conditions:The fainter parts of the Milky Way are barely visible.Haziness only visible on the horizon.Atmosphere stable with little interference.

Instrument:12-inch Dobsonian.

In this globular cluster some of the stars are well resolved in this cluster and that this cluster is slightly concentrated towards each other.In overall this cluster has a granular appearance.This globular cluster measures 3.2'x 2.4'.Chart No:348,NSOG Vol.2.

2011 July, 30th Saturday

Location:Perdeberg.

Instrument:12-inch Dobsonian Reflector Telescope.

Sky Conditions:The fainter parts of the Milky Way are barely visible.

Transparency of the Sky:Haziness only visible on the horizon.

Seeing:Atmosphere stable with little interference.

Limiting Magnitude:4.9.

NGC 6441

--------

Object Type:Globular Cluster.

First Impression:This object looks like a globular cluster.

Location:Scorpius.

Time:8:00pm.

Chart Number:No.18(Extract taken out of "Atlas of the Night Sky").

Size:26mm Eyepiece:Field Of View:57'/12=4.7'.

20mm Eyepiece:Field Of View:50'/11.5=4.3'.

4.7'+4.3'=9.0'.

9.0'/2=4.5'.

Size in Arc Minutes:4.5'(Nucleus).

Ratio:1:2.

Major Axis:4.5'(Nucleus).

4.5'/2=2.2'.

Minor Axis:2.2'(Halo).

Globular Cluster is 4.5'*2.2'.

Brightness:Magnitude 7.4.

Brightness Profile:The central nucleus of this globular cluster grows slightly brighter compared to the far outskirts of this cluster.

Challenge Rating:Fairly Easy.

Description

-----------

The stars in this globular cluster are partially resolved.This globular cluster almost looks like a small frozen snowball.There is a small chain of bright stars and these stars are centrally concentrated towards each other.

Tom Bryant

2010 7 3 23:25:36

Observing site: Pinnacles overlook

Telescope: C-11

[17h 50m 12s, -37 3' 0"] A tight, compact cluster very near a bright M (?) star. Resolved in the 12.5mm.

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