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NGC 6231 (13,914 of 18,648)

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Table of Scorpius

NGC 6231, Dunlop 499, Cl Collinder 315, C 1650-417, Cl VDBH 201, Ocl 997.0, COCD 385, Lacaille II.13, Caldwell 76, Table of Scorpius, h 3652, GC 4245

RA: 16h 54m 8.51s
Dec: −41° 49′ 36″

Con: Scorpius
Ch: MSA:1460, U2:407, SA:22

Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)

(reference key)

Type: open cluster, 13p

Mag: B=2.83, V=2.6

Size: 14′
PA: ?

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Sketches  (2)

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Photos  (1)

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History and Accurate Positions for the NGC/IC Objects (Corwin 2004)

NGC 6231. See NGC 6227.

Remarks

This bright open cluster lies in a magnificent region of sky at the point where the Scorpion's tail is attached to the body. Observed by Halley from St Helena.

Historical observations

Lacaille (1755)

Lacaille included it in his 1755 catalogue as Class II No. 13. In his half-an-inch 8x telescope he saw it as a "close group of seven or eight close faint stars."

Dunlop, James (1827)

James Dunlop observed this object from Paramatta, New South Wales, and included it as No. 499 in his catalogue of 1827. Using a 9-inch f/12 telescope, he described it as "a cluster of pretty bright stars of mixt small magnitudes, considerably congregated to thge centre, about 10' diameter, with a large branch of very small stars extended on the north side; this is 150 Scorpii."

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 "a fine bright large cluster pretty rich, class VII. 10', stars 10..13th mag. Place of a double star 5th mag, the preceding but one of 7 bright stars in the middle."

NGC/IC Dreyer (1888, 1895, 1908)

The NGC records it as "bright, considerably large, pretty rich, consisting of stars of 10th-13th magnitude." On photographs is measures 14' and is visible to the naked eye at magnitude 2.6.

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.

Trumpler, R.J. (1928)

Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 16' and the class as 1 3 r.

Burnham's Celestial Handbook

This striking and impressive object, according to Burnham, "resembles a miniature edition of the Pleiades, with a central knot of 7 or 8 bright stars. The size of this central mass is about 6' but the outlying fainter members bring the total size to something like 15'." Burnham captures the cluster well in his description of "a handful of glittering diamonds displayed on black velvet." He notes that there is very little colour in the cluster, all the brighter stars appearing brilliantly white. The cluster contains three stars brighter than 6th magnitude, seven stars between 6th-7th magnitude and six stars between 7-8th magnitude.

Doig, P. (1926)

"A Catalogue of Estimated Parallaxes of 112 Nebulae, Open clusters and Star Groups", Vol 36 (4), p 107-115.

"cluster of brihgth stars;part of irrregular cluster covering field 2 degrees square; contains nebulosity; visible to naked eye as 4.5 mag star (Gore)."

Sulentic & Tifft (1973)

The RNGC (Sulentic and Tifft 1973) notes that this is a 8.5 mag open cluster.

Photo index

Photo Index by Jim Lucyk: Burnhams V3 p1723, 1727, Vehrenberg's Atlas of DS Splendors (3ed) p171, Ast.Obj.for South.Tel. (Hartung, 1984).

Bailey, S.I. (1908)

"! cluster, fairly condensed"

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

Modern observations

Harrington, Phil

Harrington writes that "one glance will immediately tell you that this object is something special ... when viewed with an 8-inch telescope at low power, about a quarter of its stars shine between magnitudes 5 and 13. The remaining suns, all fainter and unresolved, surround these in a wedge of celestial mist. Larger apertures and higher magnifications resolves some of the cloudiness into even more stars."

Tom Lorenzin

Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "6M; 15' diameter; brilliant 5M star overlays 100-plus 10M members; cluster H-12 1.5 degrees to NE; reference- chart BCH-III-1725; add the Zeta SCO crowd and this area makes a terrific binocular field; see the field as the "Baby Scorpion" which clings to the back of its mother's tail."

Ware, Donald J

Donald J. Ware:"This cluster is only about 15' in extent, but has over one hundred stars blazing in this small area. According to Burnham's Celestial Handbook, if this cluster were the same distance from us as the Pleiades, it would appear about the same size as that cluster, but it would be about fifty times brighter, and its brightest members would shine as bright as Sirius!"

Steve Coe

Steve Coe, observing with a 17.5" f/4.5 at 100X, notes: "Very bright, large, rich, compressed and irregular in shape at 100X. This easy naked eye object is a fuzzy spot located where the curve in the scorpions' tail starts. It is an excellant binocular field that includes several bright stars and a rich mixture of dimmer members.

Rui Henriques

1997 July 06

10x50 tripod-mounted. 1997-07-06. "brightly condensed, many stars; stands very well out from background" [Rui Henriques]

Ed Finlay

1992 May 30

ASSA DSOS: Ed Finlay, observing with a Meade 4-inch ED APO refractor from Johannesburg, 1992 May 30, calls it a "splendid object at 102x."

Contemporary observations

Magda Streicher

(no date)

(8-inch Meade, 18mm Super-Wide Angle eyepiece, 36' fov)

Very bright, large extended cluster. Smaller star combination resembles the Pleiades with a nice double in the middle. The rest of the mix magnitude stars stretch in a very elongated way to the south with a bright prominent arrowhead. Resembles the body of a fly, with the brighter stars a more yellow color.

In the viewfinder it looks like a crocodile so I want to rename this cluster.... "Crocodile Cluster"

Kerneels Mulder

2008 October 25

Date and Time: 28 October 2008, 21:20
Location: Prince Albert (Western Cape, South Africa).
Instrument: Orion XT10 10" f/4.7 Dobsonian Reflector
Eyepieces: 10mm (120x, 26′ FOV), 25mm (48x, 1° FOV)
Sky Conditions: Clear. Seeing: 5/10. Transparency: Average.
Scattered clouds, humid and windy

Cluster is easily located, but it is difficult to establish the extent of the cluster.

Large open cluster with rich central region. Irregular in shape. Almost appears to have a reversed "S" shape with stars concentrated towards the center. Five bright stars are very prominent within the central region, with approximately ten fainter stars surrounding them. Approximately 50 stars can be counted without difficulty, but due to bad seeing and transparency fainter stars might not have been observed. The cluster almost fills the 1 degree field of view if stars in outer region are included. Central region is about 15 arcminutes in size. Stars of varying magnitude are visible.

Auke Slotegraaf

2008 April 11

Date: 2008 April 11, 21:15, Friday night

Location: Sutherland (quarry)

Sky conditions: Clear, moonlight.

Telescope: 12-inch f/4.9 Dobsonian

Eyepieces: 25mm Sirius Plossl, 60x, 46' fov & 10mm Sirius Plossl, 150x, 14/17' fov

While waiting for the Moon to set, I aimed the 12-inch at NGC 6231, which was pretty much on the horison at the time. Low enough, in fact, that I could comfortably sit in the camp chair and sketch the cluster.

Essentially, NGC 6231 is eight or so bright stars, arranged in a roughly east-west elongated grouping, at least 10 arcminutes long and 5 arcminutes wide. Scattered in and amongst these primary stars are about 100 fainter stars. Scattered to the south, and east, is a large field of faint stars, like a dim extension (well-shown on the DSS image).

1998 April 27

1998-04-27/28, 11x80 tripod-mounted binoculars, Die Boord. Seeing average, transparency average, dew. "A stunning, brilliant cluster of bright, white stars, 9' across. Not many other (fainter) stars seen in this grouping; modest brightness range."

1982

A 15.5-inch shows a truly beautiful cluster of 6-8 very bright members and about twenty 10th magnitude stars. Careful viewing shows many smaller stars dispersed inbetween these brighter members. The stars display a considerable brightness range, and lie well spread out. The general impression is of a triangular shape, borne out by looking at the cluster out of focus. The cluster is clearly distinguished from the background by its sheer brightness. The bright triangle of the multiple Zeta Sco lies due south in the same field of view. The cluster lies in the bend of Sco tail. The cluster is a member of the Scorpius OB 1 Association.

Chris Vermeulen

2006 March 25-26

2006/3/25-26, 0h00-03h00

Sky Conditions: Poor: Cloudy

Quality of Observation: Moderate

Ngwenya Lodge

6" Dobsonian, 25mm & 10mm Eyepieces

NGC6231 is a cluster of stars that in the tail of Scorpio. What makes this open cluster so amazing is the vast number of bright stars within this cluster. It is a rather large open cluster and it also appears that there might be some nebulosity in the cluster, but it appears very feint and is barely visible under the conditions. NGC6231 stands out very beautiful against the background of the night sky and stars. It is best viewed with a lower magnification to truly capture the full extent on the open cluster.

Gary Lillis

2007 July 25

2007 July 25, 19:20 SAST

Walmer, Port Elizabeth

2.5-inch f/7.6 refractor (EP: 25mm 28x 45arcmin fov)

Conditions: Bright Moon within vicinity.

The Northern Jewel Box. Small 15arcmin of seven stars, bright and conspicuous M2.6 apparent magnitude, appeared first to be bright small dense concentration of M3.5-4.7 in the centre of a large sparse cluster about one degree in size. NGC 6231 is small, entirely engulfed by many field stars of M3-4, the brightest of these is xi Scorpii; three bright orange giants M2 south by three-quarters of a degree. NGC 6231 is very densely concentrated without any starless patches, mingled with the starry background, moderately difficult to find through the finder scope, for reasons owing to the conditions, in a dark sky with binoculars it is relatively easy to find.

Richard Ford

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 6231

--------

Object Type:Open Cluster.

First Impression:This object looks like an open cluster.

Location:Scorpius.

Time:7:25pm.

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

Size:26mm Eyepiece:57'/6=9.5'.

20mm Eyepiece:50'/5.5=9.0'.

9.5'*9.0'=18.5'.

18.5'/2=9.2'.

Size in Arc Minutes:9.2'.

Ratio:1:3.

Major Axis:9.2'.

9.2'/3=3.0'.

Minor Axis:3.0'.

Open Cluster is 9.2'*3.0'.

Brightness:Magnitude 2.6.

Brightness Profile:Far from the outskirts of this open cluster becomes brighter.

Challenge Rating:Fantastic Sight.

Description

-----------

When I observed this open cluster I have found that this cluster is well detached with bright stars.In overall I have counted 40 stars within a fixed diameter.Although this is a young cluster with a luminosity of A and F stars which suggests that this cluster has white to yellow stars where all the bright and faint stars are mixed together.The stars in this open cluster is slightly concentrated towards each other.I have on the other hand found some starless patches around the outskirts of this cluster.On a final note I have also found a small clump of bright stars.

Tom Bryant

2010 7 3 23:57:56

Observing site: Little Bennett Regional Park

Telescope: C-11

[16h 54m 0s, -41 48' 0"] The jewel box of the Scorpion. A superb cluster of bright white and blue white stars, with a few red ones as well.

Allen Versfeld

2013 May 05, Sunday

Location: Hennops River

Time: 23:30

Telescope: C8, 30mm plossl

Limiting magnitude: 5

Sky conditions: No clouds or haze, minimal skyglow, seeing a little unsteady.

Very geometric cluster, with +- 50 white stars visible which seemed to form grid-like patterns. Perhaps 20' across.

Favourite lists

Lacaille's catalogue

The Messier objects

Dunlop's catalogue

The Bennett objects

The Caldwell list

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