sponsored by psychohistorian.org


Deep Sky Observer's Companion – the online database


Welcome, guest!

If you've already registered, please log in,

or register an observer profile for added functionality.


log in to manage your observing lists























Full database:

Entire DOCdb database of 18,816 objects.



NGC 6811 (15,803 of 18,816)


oc gc pln bn dn gx gxcl ast aka lost




finder chart

altitude today

altitude (year)


½°, , in DOCdb

Warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/yivumoo/public_html/show_object.php on line 167

Warning: fopen(/home/yivumoo/public_html/logs/showobject/20210926.txt): failed to open stream: Disk quota exceeded in /home/yivumoo/public_html/show_object.php on line 168

Warning: fwrite() expects parameter 1 to be resource, boolean given in /home/yivumoo/public_html/show_object.php on line 181

Warning: fclose() expects parameter 1 to be resource, boolean given in /home/yivumoo/public_html/show_object.php on line 182

show browsing

Hole in a Cluster

NGC 6811, Cl Collinder 402, C 1936+464, Cl Melotte 222, COCD 464, Hole in a Cluster, h 2044, GC 4505

RA: 19h 37m 10s
Dec: +46° 22′ 30″

Con: Cygnus
Ch: MSA:1109, U2:84, SA:8

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

(reference key)

Type: open cluster, 31r

Mag: B=7.47, V=6.8

Size: 14′
PA: ?

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

NGC 6811. JH has two observations of this, separated by nearly a minute of time in RA and 6 arcmin in Dec. The RA of the first observation is correct, while the declination of the second is correct. Unfortunately, the position JH adopted for the GC carries the RA of the second, and a Dec 10 arcmin further on north. I think he meant to use only the second observation (he notes that the first observation refers to "A double star in the southern part..."), so the incorrect Dec must be a transcription or typographical error.

Once these errors are corrected, though, N6811 turns out to be quite a nice cluster, ten or twelve arcmin across, with perhaps a hundred stars, many of the 10th and 11th magnitudes.

Published comments

Trumpler, R.J. (1928)

Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 13' and the class as 3 1 p.

Raab, S. (1922)

Raab, S. (1922) A research on open clusters. Lund Medd. Astron. Obs. Ser. II, 28, 1.

Discussed, based of F-A plates.

Sulentic & Tifft (1973)

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

Bailey, S.I. (1908)

"cluster, coarse"

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

Photo index

Photo Index by Jim Lucyk: Sky&Tel. 10/86 p427, The Astrograph 8-9/81 p4.

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

Walter Scott Houston

Houston (1973) notes: "A 6-inch instrument will show some 75 faint stars shimmering inside an area 15' across. It reminds some amateurs of an opera-glass view of the Beehive."

Houston notes that this small group of stars shines with a total light of magnitude 6.8. He reports a comment by Tommy Christensen, who observed it with a 3.5-inch refractor and saw a distinct "smoke ring" of stars with a centre that was conspicuously dark though not completely starless. "Since I remembered the cluster as an unimpressive, nondescript group, clearly another look was in order. At the next opportunity I examined the cluster with an 8-inch reflector. No smoke ring! I tried a 10-inch with the same result. Nevertheless, I tossed the problem out to readers ... scores of observers turned their scopes on the cluster, and responded with all kinds of descriptions - bells, butterflies, dinosaurs, a pair of fighting peacocks .. But no smoke rings .. I tried stopping down my Clark refractor from 4 to 2 inches. Lo and behold, there was the smoke ring." Houston also reports an observer in Czechoslovakia, using a Zeiss 2.5-inch refractor from 14x to 140x who saw it as "a clear-cut ring of stars with no hint of the butterfly pattern I suggested in an earlier column."

From a collection of observations reported by Houston, there is "a dark band about 5' thick running through the middle of the cluster" This impression was retained with apertures up to 11-inch, but with large telescopes the dark centre did not show.

Tom Lorenzin

Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "9M; 15' diameter; large and sparse with stars in two curving chains; 30' to SE is a smaller (7' diameter) fairly rich, faint cluster (70-plus members 12 thru 14M) with a central void; which is N6811? I don't know; do you?."

Brian Skiff

7x35mm - mod f at diffuse at first glance. attention shows a few of the brtst *s. unconcen. to immed W is br trapezoid of *s that could be mistaken for cl. BS, 28Jun1992, Hutch Mtn.

8cm - polygonal, nicely res @ 20 into 20 *s, no haze. BS, 15Sep1982, Anderson Mesa.

15cm - avg cl, 20' diam, rich in f *s m10+. 50 *s w/a bit of haze. rich bkgrnd. HM/BS, 28Jun1971, FtL.

- mod br, mod rich, annular cl fully res @ 80x. annulus 10' diam w/3' hole, outliers to 15' diam. 140x: 75 *s m10+ pretty uniformly scattered around ring. m11.5 pair SE side. m13 * in N side of annulus that seems dbl. brtr loose circlet about 1/2 deg WNW, some *s of which are plotted on U2000. BS, 17June1991, Anderson Mesa.

25cm - lg, 20' diam w/*s m9+. much seen at lox. 90x: some haze and grpings throughout cl. 60 *s.

30cm - 149x: 75 *s in 11' fld. loose. elong E-W. *s m9.5-10.5.

Contemporary observations

Magda Streicher

(no date)

Alldays (22.50S, 20.12E, 770m).

12-inch f/10 SCT (95x, 218x)

It is a very faint spacious grouping of stars with some open areas towards the middle. (With imagination if forms the letter 83 with a asterism of five stars going out from the letter 8, or may be a bicycle). Slightly elongated in a N-S direction.

Favourite lists

Lacaille's catalogue

The Messier objects

Dunlop's catalogue

The Bennett objects

The Caldwell list

Named DSOs

Object search

First search phrase


Second search phrase

Type of object to include:

open cluster
globular cluster
planetary nebula
bright nebula
dark nebula
galaxy cluster
asterism & stars

The Bug Report

DOCdb is still in beta-release.

Known issues, feature requests, and updates on bug fixes, are here:

> Bug Report


Found a bug? Have a comment or suggestion to improve DOCdb? Please let us know!

> Contact us


DOCdb is a free online resource that exists to promote deep sky observing.

You could help by sharing your observations, writing an article, digitizing and proof-reading historical material, and more.

> Find out more

Everything on DOCdb.net is © 2004-2010 by Auke Slotegraaf, unless stated otherwise or if you can prove you have divine permission to use it. Before using material published here, please consult the Creative Commons Attribution-Non-Commercial-Share Alike 2.5 License. Some material on DOCdb is copyright the individual authors. If in doubt, don't reproduce. And that goes for having children, too. Please note that the recommended browser for DOCdb is Firefox 3.x. You may also get good results with K-Meleon. Good luck if you're using IE. A successful experience with other browsers, including Opera and Safari, may vary.

Warning: Unknown: open(/tmp/sess_546f1a64993f2ddb6ba1d26dc128af66, O_RDWR) failed: Disk quota exceeded (122) in Unknown on line 0

Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct () in Unknown on line 0