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NGC 6681 (15,316 of 18,816)

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NGC 6681

NGC 6681, Dunlop 614, C 1840-323, GCl 101, Messier 70, Bennett 115, h 3756, GC 4428

RA: 18h 43m 12.64s
Dec: −32° 17′ 30.8″

Con: Sagittarius
Ch: MSA:1413, U2:378, SA:22

Ref: SIMBAD, SEDS

(reference key)

Type: globular cluster

Mag: B=9.76, V=9.06

Size: 8′
PA: ?

Historical observations

Messier, Charles

This small globular cluster was discovered by Messier in August 1780. He described it as "a nebula without star, near the preceding [M 69] and on the same parallel. Near to it is a 9 mag. star and four small telescopic stars, almost in the same straight line, close to one another and situated below the nebula as seen in a reversing telescope. Diam. 2'."

William Herschel (c.1784)

In the Appendix to the 1912 'Scientific Papers of Sir William Herschel' this object is described as "1784, July 13. easily resolvable, cB, pL, iR, a very faint red perceivable."

Dunlop, James (1827)

James Dunlop observed this object from Paramatta, New South Wales, and included it as No. 614 in his catalogue of 1827. Using a 9-inch f/12 telescope, he described it as "."

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, gmbM, diam in RA = 7 seconds; resolved into stars 14..17m." On a second occassion he called it "globular, B, R, gbM, resolved into stars 15m."

Published comments

Doig, P. (1925)

Journal BAA, 36(3), Dec, p91

3.5' diam.

Burnham's Celestial Handbook

The Herschels found M 70 to be a compact globular, with stars 14-17 magnitude, and a bright condensed centre. The appearance is very similar to that of M 69; on Lowell Observatory 13-inch camera plates, notes Burnham, M 70 seems slightly the fainter of the two, and also somewhat more irregular in outline, with a more granular or "clumpy" structure around the outer edges. The 9th magnitude star mentioned by Messier is 14' to the west and a little south. On the NE edge of the cluster there is also a small extending arc of stars described by K.G. Jones as "a little slightly curved 'tail' of small stars, shooting off like sparks to the NNE. These may be the stars mentioned by Messier." This group consists of a small clump connected with the cluster, plus two brighter field stars.

Sulentic & Tifft (1973)

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

Harris, W.E. (1997)

RA 18 43 12.7 (2000) Dec -32 17 31 Integrated V magnitude 7.87 Central surface brightness, V magnitudes per square arcsecond 15.28 Integrated spectral type F5 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 2.50c: Core radius in arcmin .03. ["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) ]

Bailey, S.I. (1908)

"globular cluster, fairly condensed"

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

Melotte, P.J. (1915)

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

Modern observations

Hartung, E.J. (1968) Astron.Obj.South.Tel

Hartung finds an aperture of 6-inch necessary to resolve stars in this cluster, and goes on to describe it as a "bright round compact well-resolved cluster with outliers about 1.5' across, and lies in a fine starry field." He notes that a 3-inch telescope shows it as an easy hazy spot.

Moore, S. (1992)

Stewart Moore (Fleet, Hampshire, UK), observing with a 12-inch f/5, writes in the The Webb Society Nebulae and Clusters Section Report No. 10, July 1992: "Not resolved at powers up to x250. Although a featureless object it is nevertheless a pleasing cluster in an attractive field."

Tom Lorenzin

Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "8M; 4' diameter; unresolved round glow with much brighter core; a rather cool lick of flame for SGR's Teapot."

Steve Coe

Steve Coe, observing with a 13" f/5.6, notes: "(M 70) Bright, large, round and has a very bright middle at 100X. This globular has 10 stars resolved at 220X and there is a curved band of stars within the cluster that form an arc from the core to the NW edge, in a PA of about 45 degrees. This chain of stars is brighter than the general glow of the cluster. M 70 really grows with averted vision. It is easy in the 11X80 finder."

Contemporary observations

Auke Slotegraaf

2016 October 30, Sunday

Location: Night Sky Caravan Farm, Bonnievale.

Date: 2016 Oct 30, Sunday.

Time: 22:35 SAST

Telescope: Little Martin (4-inch f/6.5 Celestron refractor)

11mm Nagler Type6 (60x): Reasonably faint, pretty small globualr cluster. Two small (11.5-mag.) stars lie near the north-eastern edge of the cluster. A strand of (4) stars trails off for 11' to the north-east.

1993 April 30

30/04/93: Observing with a 6-inch f/8.6 Newtonian at 52x, the one-degree field centered on this globular makes a very attractive sight. It shares the busy field with 2 straight lines of four stars, which lie to the south of the cluster. One chain, running west-east, is made up of 9th mag stars, while the second chain (lying NE-SW) consists of 10-11th mag stars. On the western edge of the field, and slightly south, lies an 8th mag double star, which has a vF companion SE. As if to break the austere linearity and add a bit of chaos, there is a third line of four stars, starting to the NE of the cluster and winding irregularly towards the cluster. This line is K.G. Jones' "sparks to the NNE." The cluster is a really intriguing and beautiful object -- must be wonderful in the 15.5-inch. The 6-inch at 144x shows 2 small stars on the NE edge of the cluster. Is there perhaps a small star on the SE edge of the cluster, or is the cluster perhaps not evenly concentrated?

1997 July 09

1997 July 9, Wednesday, 20:00 - 22:00 Jonkershoek. 11x80's tripod-mounted. Moderate conditions. Similar to NGC 6637, M69. Forms one corner of a Corvus-shaped asterism of 8-9th mag stars.

Magda Streicher

(no date)

Location: Campsite (South 23 16 East 29 26).

Sky conditions: Clear, steadiness good.

Instrument: Meade 8 inch, Super wide-angle, 18mm eyepiece; 36.2' fov

DSO Report N

Medium size, considerably bright, round, compressed globular cluster, brightens to a starlike core. A few stars running out to the north to show the way to some brighter stars. About 3 to 4 arc minutes in size.

(no date)

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

Relatively small, considerably bright, round, compressed globular, brightens slowly to a star-like core. With careful observation short faint star strings can be seen running out to the north to show the way to brighter stars in the field of view (95x). This globular shows character and reminds me of a bug with a round body and two prominent tentacles that extend outwards towards the west. The brighter of the two is in the northern direction and the fainter one towards the south. Messier discovered this object in 1780.

Richard Ford

2015 August, 9th

Location:Perdeberg.

Time:8:58pm.

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 the stars are partially resolved and that the stars in this cluster is slightly concentrated towards each other.In overall this clusters shape looks like a bright uniform snowball.The nucleus of this globular cluster is strongly condensed.This globular cluster measures 4.3'x 3.3'.Chart No.327,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.

M70

---

Object Type:Globular Cluster.

First Impression:This object looks like a globular cluster.

Location:Sagittarius.

Time:11:10pm.

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

Size:26mm Eyepiece:Field Of View:57'/16=3.5'.

20mm Eyepiece:Field Of View:50'/14=3.5'.

3.5'+3.5'=7'.

7'/2=3.5'.

Size in Arc Minutes:3.5'(Nucleus).

Ratio:1:3.

Major Axis:3.5'(Nucleus).

3.5'/3=1.1'.

Minor Axis:1.1'(Halo).

Globular Cluster is 3.5'*1.1'.

Brightness:Magnitude 8.1.

Brightness Profile:From the far outskirts of this globular cluster it grows brighter towards the nucleus.

Challenge Rating:Very Easy.

Description

-----------

This globular cluster is partially resolved as most globular clusters are concerned although towards the outskirts of this cluster I have found some chains of bright stars that are resolved.However on the other hand the stars in this globular cluster is centrally concentrated towards each other.

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