sponsored by psychohistorian.org

DOCdb

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.

List:

log in to manage your observing lists

 browse:

 

 position:

 

 next:

 

 options:

summary

rename

prune

trim

remove

close

copy

combine

plan

bookmark

load

new

delete

marathon

favourite!

Full database:

Entire DOCdb database of 18,816 objects.

 browse:

 position:

NGC 2808 (5,966 of 18,816)

 next:

oc gc pln bn dn gx gxcl ast aka lost

Object:

list

bookmark

finder chart

altitude today

altitude (year)

 search:

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

show browsing

NGC 2808

NGC 2808, Dunlop 265, C 0911-646, GCl 13, Bennett 41, h 3152, GC 1793

RA: 09h 12m 2.57s
Dec: −64° 51′ 46.2″

Con: Carina
Ch: MSA:1007, U2:448, SA:25

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

(reference key)

Type: globular cluster

Mag: B=7.77, V=6.89

Size: 14′
PA: ?

Image gallery

Sketches  (3)

Select a sketch and click the button to view

Photos  (1)

Select a photo and click the button to view

Historical observations

Dunlop, James (1827)

James Dunlop discovered the globular cluster while observing from Paramatta, New South Wales, and included it as No. 265 in his catalogue of 1827. Using a 9-inch f/12 telescope, he described it as "a very bright round nebula, about 3' or 4' diameter, very gradually bright to the centre. This has a fine globular appearance."

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 cluster, extremely compressed pretty gradually very much brighter to the middle; up to a perfect blaze; diam. in RA = 26.8 seconds; stars of 16th magnitude; equal. R.A. doubtful; the mirror being in a spring case (afterwards disused)." On the second occassion he described it as "globular cluster, 4' or 5' diameter first pretty gradually then pretty suddenly brighter to the middle; all resolved into stars 16 mag and a few 15 mag. A neat double star follows distance 1 field." His next observation records it as a "superb globular cluster, diam = 5', very much compressed almost to a nipple. Stars innumerable and very small; 13..15 magnitude." His final observation notes it as being "a truly beautiful and delicate globular cluster; diameter in RA = 45 seconds, that of the most compressed part 15 seconds; gradually very bright in the middle; all finely resolved into perfectly equal stars like the finest dust, which are seen with the left eye without effort, but the right requires to be somewhat strained to discern them. Runs up to a blaze in the centre."

NGC/IC Dreyer (1888, 1895, 1908)

The NGC records it as "remarkable object, globular cluster, very bright, extremely rich, very gradually extremely compressed in the middle, 45 seconds diameter, consisting of stars 13..15 mag."

Published comments

Bailey, S.I. (1908)

"!! globular cluster, 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.

Doig, P. (1925)

Doig, P. (1925) Notes on the nebulae and clusters in Webb's 'Celestial Objects for Common Telescopes' (Sixth edition, Vol.ii). Part III. Southern Objects. M.N.R.A.S., 36(3), 91.

Harris, W.E. (1997)

RA 09 12 02.6 (2000) Dec -64 51 47 Integrated V magnitude 6.20 Central surface brightness, V magnitudes per square arcsecond 15.17 Integrated spectral type F7 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 1.77 Core radius in arcmin .26. ["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) ]

The mean blue magnitude of the 25 brightest stars, excluding the 5 brightest, is 15.09.

ASV Journal, Vol 24, No 3, June 1971: "good in binoculars or telescope."

Sulentic & Tifft (1973)

The RNGC (Sulentic and Tifft 1973) notes that this is a 8.0 mag globular cluster.

Modern observations

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

Hartung writes: "In a fine field this beautiful object is a splendid example of the symmetrical strongly compressed type of globular cluster, composed of innumerable faint stars. It is about 5' across and a 6-inch will resolve it; to smaller apertures it is a bright nebulous haze with strong central condensation."

Sanford (1989) Observing the Constellations

Sanford calls it a "richly concentrated ball of stars in a 10-inch."

Brian Skiff

Alcaino & Liller: m11 * W: V=10.43/0.15, ~3' WNW of center.

Harris: m11 *: V=10.45/0.16.

White: pair E: V=9.95/1.68, 10.54/1.54.

15cm - br well concen cl of hisfcbr @ 50x, where it is fntly gran. 195x: partially res into many hundreds of vf vsm *s---powdered sugar texture. strong even concen except nuc, which is sl sharper. 50x shows sub*ar nuc, but merely smooth and br @ 195x. outliers reach as far as m11 * due W, but seem to go farther N&S, although fld *s SE confuse things. main body half this diam; no well-def core or nuc. wide pair 10' E. BS, 18Feb1990, LCO.

Head, Marilyn

"10 Easy Globs!" by Marilyn Head (105 Owen Street, Newton, Wellington, Aotearoa / New Zealand; mhead@clear.net.nz)

NGC 2808 in Carina and NGC 3201 in Vela are two very different globs easily found by using the false cross as a reference. NGC 2808 is halfway between Iota and Beta Carinae and is like a miniature 47 Tuc., very bright and compact. Harlow Shapley (who incidentally used globulars to establish the shape of the Milky Way, albeit making it twice as large as it really is) classified Globulars by their concentration of stars correlated with the central surface brightness from I to XII , class I , to which 2808 belongs, being the most highly condensed. NGC 3201 provides the contrast, being a class X globular which can be found by following the line between the two stars, Delta and Kappa Velorum, upwards.

James, Andrew (1998+)

From: "Neat Southern Planetaries - IX."

NGC 2808 / 256/ GSC0911-646) (09120-6452) (Carina) is the tenth brightest Globular Star Cluster (GSC) in the sky first discovered by Dunlop and was extensively observed by John Herschel in 1836. Between magnitude 6.1 and 6.3, it should be just visible to the naked eye, though some optical aid is required to reveal it as non-stellar. Some debate still exists on the naked-eye visibility Greg Bryant in (Universe 43,12 & 44,1 (1996-97)) in his article entitled 'Naked-Eye Globular Clusters' states in Table 2 that NGC2808 is a possible naked-eye cluster. In the number of observations of this object, I have to admit my eyes cannot claim to have seen NGC 2808 visually, with the last time being April 1997 from Mt. Banks. In size it covers some 7'min.arc. with the outliers being up to 13.8'min.arc. from the core's centre. The NGC classification by Dreyer in 1888 is given as 'L,vB, eRi, eCM' - large, very bright, excessively rich, extremely compressed in middle. In the same field, some 9.5'min.arc. ESE is the John Herschel pair HJ4164 (09135-6455) first measured by Russell in 1879. The stars are magnitude 10.0 and 10.6, separated by 16.4"sec.arc. along position angle 64O.

The 'southern' superlatives given to this magnificent cluster are numerous. For example, the general 1920's text of Webb's 'Celestial Objects for Common Telescopes', has on pg.299 a quote by R.T.A.Innes;

"Superb cluster (with) 13th to 15th magnitude stars....like the finest dust, centre blaze."

David Frew 'March Deep Sky Objects' (Universe 30,3 1986);

"This beautiful mag. 6.3 globular star cluster is a much underrated object and is even visible to the naked eye from dark inland skies. A 15cm. telescope will begin the resolution, as the brightest giants are of Mag.13. The overall diameter is about 4' to 5', though the condensed centre is less than half of this. The distance is about

30 000 [light years]."

Andrew Murell (Universe 42, 3 1995) in his article entitled 'Carina';

"NGC 2808 is one of the best globular star clusters in the sky, appearing like a cross between Omega Centauri and 47 Tucanae. The cluster is about 14' in diameter and can be fully resolved in a 12" (30cm.), with the outer regions resolved in an 8". It is quite bright, having an integrated magnitude of 6.8."

J Graham Little in 'Ten O'Clock High' (Southern Sky 1,4 pg.53 March/April 1994) states; "The only Globular Cluster of Carina... [and] is visible as a small, fuzzy spot in binoculars. A 15cm. 'scope is required, however, for stellar resolution, as the brightest stars are around magnitude 13. This cluster looks good through a telescope. A sprinkling of tiny stars surrounds a very dense, bright centre. I have noticed on nights of good viewing what appears to be dark lanes towards the extremities of the cluster."

Burnham's 'Celestial Handbook', amazingly does not describe NGC 2808, though it does appear in the object summary on pg.464. It is extraordinary the number of 'standard' texts that do not add this wonderful cluster. This could be expected, as the cluster is in the shadow against the more memorable GSC's of Omega Centauri and 47 Tucanae. It is also in brightness only a few tenths of a magnitude below the vastly overrated northern 'Great Cluster' in Hercules (M13). Observationally, the centre of the cluster is both very condensed and very bright, when compared with the cluster as a whole. To my eyes it appears to have features similar to 47 Tucanae, with the star

counts rising exponentially towards the centre. To quote from AOST1;

"[This] beautiful object is a splendid example of the symmetrical strongly compressed type of globular cluster, composed of innumerable faint stars....to small apertures it is a bright nebulous haze with strong central condensation."

My first observation was past members' Beryl van Heast 10.5cm. (4") Newtonian at Bowen Mt. 13.35 UT; 30th December 1978. My observation log states;

"Very bright with a very dense core of unresolved stars, especially [towards] the core. Wonderful!"

It is one of only three known Class I's, and it is the closest of all these by a factor of four! GSC Classes are based on the concentration of stars as seen in the telescope, which was first proposed by Shapley and Sawyer in 1926; where 'I' is highly concentrated, while 'XII' is loose and scattered. Class 'I' label is rather deceptive for NGC 2808. Easily separated in a 15cm, the outer portions of the cluster appear even. Separation of the 'core' stars is a bit more difficult. A 30cm. may just see some of the centre stars, and a 40cm. perhaps will start to break apart the core. Sulentic and Tufft's 1973 revision of the NGC (RNGC) and Roger Sinnott's NGC 2000.0 classification correctly and aptly gives the description; "!Globular Star Cluster, very large, extremely rich, very gradual, extremely compact in centre, 45'min.arc. diameter (core), stars 13....15."

It has proved difficult to determine distanceof this cluster because of the sheer concentration of stars, and as such, information sources vary considerably. Harlow Shapley in 1930 estimated the first distance at 16.2kpc. Lack of variables, especially RR Lyraes, also make distance estimates nearly impossible. Variables are the keys to cluster distance determinations. The first variable was discovered in the early 1930's. By 1962, Sawyer and Hogg had increased this number to four, and yet all remained without known periods until the 1970's. Due to the lack of observations and of star counts, another observational programme was again seriously undertaken by King in 1968 - yet he found no new variables. By 1973, the number of variables increased from four to nine from observations at Mt.Stromlo. Distance is currently estimated to be about 11.2 kpc. (36 000 lty.), which closely approximates the estimate 11.5 kpc. in 1975. AOST2 quotes c.7.5 kpc., which is likely a bit of an underestimate of its distance. I assume David Frew has taken this value from Hogg's (1956) distance of 7.6kpc., as I could not identify his actual source. Sky Atlas 2000.0 quotes a distance of 9.2 kpc.

In 1963, the first energy distribution was measured and published by Aller (AJ, 68, 69). The globular star cluster was determined to be G2 III, later revised to an F8 type in 1967. These observations also gave an accurate radial velocity of 104 km.sec.-1 in recession.

Age is determined either by H-R Diagrams or by the Iron to Hydrogen ratio or [Fe/H]. The value for NGC 2808 is -1.37, poorer than the Sun, while the Metals to Hydrogen [m/H] ratio is -1.47. Like most globulars, the age is estimated to be between eight and twelve billion years.

At the end of 1990, the Australia Telescope looked in a number of selected globulars for Hydrogen emissions at the 21cm. line. NGC 2808 actually showed an indication of nebulose Hydrogen. This discovery has been questioned with some vigour, because globulars were suspected to be old objects that used their Hydrogen in the first few billon years when the galaxy was formed. Long ago most of the Hydrogen should have been used up, yet this globular seems to mock the 'standard' theory.

Contemporary observations

Auke Slotegraaf

1984

This bright globular cluster lies between the False and Diamond Crosses in the southern milky way. In 11x80 binoculars it appears as a bright, extended, diffuse patch, easy to see even while sweeping.

1983

Observing with a 15.5-inch at 220X, this very beautiful globular cluster looks much like a smaller version of 47 Tucanae. Its stars are crowded towards a dense nucleus, and then gradually fade to the edges, finally disappearing about 3 nucleus-diameters away. A breathtaking spectacle, the stars are very densely packed together, and the gradual thining out from compact nucleus to black sky is beautiful.

1998 January 01

1998-01-26/27, 6-inch f/8.6 Newtonian, Stellenbosch Rifle Range site. A very bright, woolly cluster, 6 arcmin across, with a central even bright disk (nucleus) 1.2 arcmin wide (5 nuclei span the width of the cluster). There is no resolution at all, not even mottling across the disk. Several faint field stars congregate near the cluster; much further out, 12 arcmin east of the nucleus, is a close double star.

1998 February 23

1998-02-23/24, 6-inch f/8.6 Newtonian, Stellenbosch Rifle Range site. 6.0 (naked eye), seeing very good. In the sweeper eyepiece, the 6-inch shows a bright globular cluster on a large and small field. The cluster brightens gradually to a broad centre (nucleus 1/5 of diameter). Cluster spans 1/4 of the Or4 field of view.

Magda Streicher

2008 June 13

NGC 2808 Carina

Tel: 16" S/C 102x - 127x - 290x - Date: 13 June 2008 - Site: Pburg - Good

Well displayed as uniformly mottled snowball of bright individual stars radiating slightly away from the outskirts of this globular cluster. Becomes centrally concentrated towards the core, which grows brighter with areas of even graininess of stars. Then nucleus fairly large as most globular cluster are concerned. In the outer region prominent chains of stars are noticeable which displays empty gaps of starless patches.

----------------

(no date)

8-inch f/10 SCT (EP: 1.25-inch 26mm SP 77x 41' fov; 1.25-inch 18mm SW 111x 36' fov) and 12-inch f/10 SCT (EP: 2-inch 40mm SW 76x 53' fov; 2-inch 14mm 218x 23' fov)

Remarkably large and round globular, which gradually brighten to a small strong, outstanding dense pinpoint core. The outer ring appears misty and ruff with faint stars, which mingle in the fairly busy surrounding star-field (76x). A few outstanding stars are situated on the south edge. Approximately 10' arc minutes towards to east a stately 8 magnitude visual double star can be seen.

1998 February 27

Location: Campsite (23 16 South 29 26 East)

Sky conditions: 7 magnitude clear.

Instrument: Meade 8" (Super wide angle 18mm eyepiece)

Date: 27 February 1998.

Meade 8" (Super flossel 26mm) Field of view 40.6 arc minutes.

Faint, Compressed, round, large mottled globular with bright and faint stars. Very dense and bright core. Stars stretches out in a haze with bright stars in the field.

1997 April 5

Location: Campsite (23 16 South 29 26 East)

Sky conditions: 7 magnitude clear.

Instrument: Meade 8" (Super wide angle 18mm eyepiece)

Date: 1997 April 5

Remarkably large and round globular, with a compressed middle, which is very dense and packed with faint stars. Edges are slightly gaseous, with a few bright stars around this globular cluster in a not so busy starfield. I estimate this globular cluster about 6 magnitude in brightness.

Chris Vermeulen

2007 June 09

2007/6/9, 17h50

Sky Conditions: Clear

Quality of Observation: Very Good

Bill Hollenbach's Pad

6" Dobsonian, 25mm & 10mm Eyepieces

This globular cluster lies in a very rich star field in the constellation of Carina. Nonetheless it clearly stands out amongst the stars in the field of view. It shines very bright with a very dense core and towards the outer edge the stars are somewhat more loosely grouped giving the impression of a surrounding halo. Similar to Omega Centauri (NGC 5139) it is also visible with the naked eye, but best observed with a telescope that reveals its dense core and 'star halo'.

Carol Botha

2007 March 10

Date: 2007 03 10, 21:40

Location: Bellville

Instrument: 8-inch Dobsonian, 17mm eyepiece

Sky: Clear; bad light pollution

Notes: Globular cluster in Carina. Bright nucleus surrounded by fuzzy haze. Just as I was about to give up on finding this object in a bad light polluted sky there it was no mistaking this mini 47 Tuc.

Richard Ford

2015, February, 22nd

Location:Perdeberg.

Time:11:59pm.

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.

This globular cluster has the shape of a large uniform snowball in appearance and that the stars in this cluster are very well resolved.The central nucleus of this globular cluster is fairly condensed and that the stars in this cluster are strongly concentrated towards each other.This globular cluster measures 5.1'x 3.9'.Chart No.46,NSOG Vol.3.

2010 February 14,Sunday

Location:Koornlandskloof.

Instrument:12"Dobsonian Reflector Telescope.

Sky Conditions:Dark moon and stars magnitude 6 and fainter are barely visible with the naked eye.

Transparency of the Sky:The most clear sky possible.

Seeing:Excellent clean sky,limited star flickering and brilliant objects.

Limiting Magnitude:6.5.

First Impression:Globular Cluster.

Location:Volans.

Chart Number:No.16(Extract taken out of "Atlas of the Night Sky").

Size:26mm Eyepiece:Field Of View:57/7=8.1'.

20mm Eyepiece:Field Of View:50'/6=8.3'.

8.1'+8.3'=16.4'.

16.4'/2=8.2'.

Size in Arc Minutes:8.2'.

Size of nucleus vs.halo:7/8.2'=0.8'.

6/8.2'=0.7'.

0.8'+0.7'=1.5'.

Size of halo:0.7'.

Brightness:Very Bright.

Brightness Profile:High Surface Brightness.

Challenge Rating:A stunning sight to observe in a large telescope under very dark skies.

Description

-----------

The bright individual stars in this globular cluster seen in this cluster suggests that the stars in this cluster are partially resolved.The stars in this globular cluster are spherically concentrated towards each other almost like a fluffy dog or snowball.Towards the central outskirts of this cluster there are slight chains of bright stars although this globular cluster somewhat presents a slightly compact appearance.No starless patches are observed.

Favourite lists

Lacaille's catalogue

The Messier objects

Dunlop's catalogue

The Bennett objects

The Caldwell list

Named DSOs

Object search

First search phrase

    and

Second search phrase

Type of object to include:

open cluster
globular cluster
planetary nebula
bright nebula
dark nebula
galaxy
galaxy cluster
asterism & stars
unverified/lost
nova

The Bug Report

DOCdb is still in beta-release.

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

> Bug Report

Feedback

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

> Contact us

Help!

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.