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NGC 6818 (15,862 of 18,816)

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Little Gem Nebula

NGC 6818, PK 025-17 1, PN Sa 2-392, PN G025.8-17.9, HD 186282, Bennett 123, Little Gem Nebula, IV 51, h 2047, GC 4510

RA: 19h 43m 57.84s
Dec: −14° 09′ 11.9″

Con: Sagittarius
Ch: MSA:1339, U2:297, SA:16

Ref: SIMBAD

(reference key)

Type: planetary nebula

Mag: B=?, V=9.3

Size: ?
PA: ?

Remarks

This small planetary nebula lies about 36' north and slightly west of Barnard's Galaxy, NGC 6822.

It was nicknamed the Little Gem by John Mallas in Astronomy magazine (August 1977, page 44.)

Historical observations

William Herschel (c.1784)

Synonyms: H IV-051

Discovered in 1787 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a cB, small, beautiful planetary nebula; but considerably hazy on the edges, of a uniform light; 10 or 15 arcseconds diameter, perfectly round. I shewed it to M. de la Lande."

Burnham, S.W. (1894)

Burnham, S. W. () "Measures of planetary nebulae with the 36-inch equatorial of the Lick Observatory", Pub. Lick Obs., vol 2, p159-167. "This seems to present a true planetary appearance, but there is no central star. There appear to be two or three slight condensations of nebulous mater, which at first glance might be taken tfor faint stars, but I do not think they are real stellar points."

Innes, R.T.A

Innes, in Union Obs. Circ., 1-44, p 345, notes: "= BD -14° 5523. About 8th mag., 5'' or 6'' in diameter. Planetary. Some very faint stars near. 1917, Sept. 13"

NGC/IC Dreyer (1888, 1895, 1908)

The NGC entry reads: "Bright, very small, round."

Published comments

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 IV. M.N.R.A.S., 36(2), 58.

Helwan Obs. Bulletin No 9 (1912)

[see also NGC 6723]

vB, S, vlE 0 deg, planetary, brihgter on the following than on preceding side. No central star or internal structure discernible with any length of exposure.

Sulentic & Tifft (1973)

The RNGC (Sulentic and Tifft 1973) notes that this is a 10.0 mag planetary nebula.

Modern observations

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

Hartung notes that even a 3-inch telescope will show this planetary, and calls it "large and conspicuous [for a planetary nebula], pale grey blue with even light and no visible central star, nearly 25" across and somewhat elliptical."

Sutherland Astron. Soc. (NSW, Australia)

In the online Southern Observer (article "The planetary nebulae of Sagittarius") this planetary is recorded as: " Is the brightest (at mag 9.3) offering in this issue's pickings. The 20" slightly elliptical disc is quite definitely dimmer toward the centre, though this dimming is nowhere as dramatic as M57, the most famous annular planetary nebulae. The hue is grey with a touch of blue. No central star is evident in 25cm. A very pleasing sight. To find: Go to the NE corner of Sagittarius and locate 55 Sagittari. The nebulae is 2 low power fields N and in the same field as Barnards galaxy (NGC 6822). RA 19.45 Dec -14.8. Winter."

Walter Scott Houston

Houston comments that "In the mid-1980's my left eye saw this object as a deep green colour, while my right eye, which had recently had its lens removed in a cataract operation, shows a vivid blue." In 1971 he wrote: "This green sharp-edged glow, about 22x15 arcseconds in extent, is immediately recognizable as a planetary of mag 10 or perhaps somewhat brighter, when viewed in a 6-inch. Its appearance is stellar in 10x50 binoculars."

Tom Lorenzin

Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "10M; 20" diameter; very small but bright, greenish and round; Barnard's Galaxy N6822 45' to SSE."

Ware, Donald J

Donald J. Ware:"Another planetary nebula, about 15-20" in diameter with a definite blue-green color to it. It is slightly extended in the north-south direction, and annularity is hinted at with averted vision."

Hogsten, Scott (IAAC)

(IAAC) Obj: NGC 6818 - Inst: 12.5" f5 Dob

Observer: Scott Hogsten

Your skills: Intermediate (some years)

Date/time of observation: Aug 19,1998 11:00 EDT

Location of site: McConnelsville, Ohio (Lat 39N, Elev )

Site classification: Rural

Sky darkness: 6.5 Limiting magnitude

Seeing: 8 1-10 Seeing Scale (10 best)

Moon presence: None - moon not in sky

Instrument: 12.5" f5 Dob

Magnification: 125x, 200x

Filter(s):

Object(s): NGC 6818

Category: Planetary nebula.

Class:

Constellation: SGR

Data: mag 10 size 22"x15"

Position: RA 19:44 DEC -14:09

Description:

Nice small but bright PN, At 200x there was some ring structure apparent

--

Brian Skiff

Subject: [amastro] Dwarfs in a dwarf telescope

I spent a bit more time last night (5 Sep UT) casting about with the Pronto at Anderson Mesa on another excellent post-monsoonal night. Among the targets were some low-surface-brightness Local Group dwarf galaxies: in decreasing order of brightness NGC 6822, IC 1613, and the Wolf-Lundmark-Melotte galaxy. At about mag. 9 and mean surface brightness about mag. 14.5/square arcmin, NGC 6822 was readily spotted at 30x. IC 1613, a magnitude fainter, was a marginal object, and WLM, somewhat fainter still by the specs, was apparently a bit too faint and I couldn't reliably see it. I'd like to try WLM again perhaps from a more southerly location.

In the field with NGC 6822 is the bright planetary NGC 6818. Since this was substellar at 30x, I estimated its brightness (without filters) with respect to the mag. 8 star west (HD 186107) as about 0.6 mag. fainter. This star has V=8.1, but is quite red, B-V=1.7, so assuming the 0.2(B-V) factor to get visual magnitudes, the planetary comes out right at mv=9.0, perhaps slightly brighter than Marling's mv=9.3. One might also make an estimate wrt the fainter star east (HD 186368, V=9.5/B-V=0.3), since its color is more neutral.

I also looked at NGC 6760 in Aquila. This was comfortably faint for the Pronto. The halo reaches roughly to a relatively bright star on the NE side of this cluster. This is mentioned by Luginbuhl & Skiff as mag. 10.5, but is actually mag. 12 or 12.5 (Kepple & Sanner also wrong.) This star was used by several 19th century observers (Winnecke, Lord Rosse, Bigourdan) as an astrometric reference; Bigourdan also calls it mag. 12 or 12.2 in two of his four observations.

While poking around near NGC 6760, I came across what appeared to be a large "absorption hole" starcloud and a tiny fuzzy knot half a degree north of it. After refinding it from 6760 with atlas in hand, I was surprised to learn that these were NGC 6755 (starcloud) and NGC 6756 (knot). NGC 6755, although a nice object at 30x, has what is to me a distinctly non-open-cluster appearance (luminosity function not right)---I'd be willing to bet this is nothing more than a starcloud. NGC 6756 was inscrutable, simply too small and faint for the Pronto at 60x.

Brian

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

Steve Coe

Steve Coe, observing with a 13" f/5.6, notes: "Bright, pretty small and little elongated. It is a lovely, light green at all powers. This planetary was obviously non-stellar at 100X. Going up to 320X, it looks somewhat like the CBS eye, with a subtle central bright spot that was never stellar. Three dim stars surround the nebula."

(unknown)

(PK25-17.1) Mag=9.3. ANOTHER "Little Gem" Nebula, in Sagittarius: 19h, 44m; -14° 9' Frankly, we revelled in getting a view of nearby faint and elusive Barnard's galaxy (NGC-6822) even more than we enjoyed seeing this medium- sized (20"+) annulus. We agreed with Ferguson that the central region of this planetary seemed darker than the outer envelope. In a sky with a 'seeing rating' of 7 - 8 (extremely calm), despite a little light pollu- tion, this "little gem" had sufficient detail and contrast to be noted as being distinctly sharper and more defined on the NW side. Another very apt description, confirmed by this observer, was the entry in the Skiff & Luginbuhl "Observing Handbook and Catalogue of Deep-Sky Objects": This object is a fairly bright bluish spot in 15 cm [aperture scope]. At 100 x the edges are sharply defined, and an indistinct dark streak seems to run through the center. At 250 x [a] 25 cm [aperture] scope shows a smoothly textured circular nebula with a slightly dimmer center. A mag. 12.5 star is visible 40" NW; another lies 1' ENE. This planetary definitely does NOT require a gigantic telescope in order to make meaningful observations of its nature!

Contemporary observations

Gabriel Giust

1994 September 08

8-inch Newtonian, 66x: 1994-09-08 "Very bright, regular and circular disc. No structure is seen within the nucleus." [Gabriel Giust, San Isidro, Argentina]

Auke Slotegraaf

2016 October 30, Sunday

Location: Night Sky Caravan Farm, Bonnievale.

Date: 2016 Oct 30, Sunday.

Time: 22:45 SAST

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

19-mm Panoptic (35x): Suspicious-looking moderately bright star.

19-mm Panoptic+Powermate (87x) and 11-mm Nagler+Powermate (150x): Confirmed as having a supra-stellar disk; and also similar magnitude stars nearby focus sharply.

1995 May 26

1995 May 26, 03:00. 11x80 binoculars. Readily seen as a star of 9th magnitude. Does it appear to have an envelope??

1995 June 01

1995-06-01: 11x80. Kelsey Farm. 23:00 SAST. Easy to see as a 9th mag star - in fact I was using it to starhop to galaxy NGC 6822 before I realized I was using it!

1997 July 06

1997 July 6, Sunday, 21:00 - 23:00 Jonkershoek. 11x80's tripod-mounted. Bright and easy, like a * 9.

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

Resembles a faint Uranus, round, medium to large in size. The disk an even gray blue color. No central star, just two stars to the east following.

(no date)

12-inch f/10 SCT (EP: 2-inch 32mm SW 95x 42' fov; 2-inch 14mm UW 218x 23' fov; 2-inch 8.8mm UW 346x 15' fov)

Resembles a faint planet Uranus. Round, with an even grey-blue colour. The ringed periphery of the planetary is hazy and soft with darker inner area observed with averted vision. No central star, just two 12th magnitude stars to be seen towards the west and northwest.

Richard Ford

2016, June, 4th

Location:Perdeberg.

Time:11:45pm.

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 oval planetary nebula's disk is seen at both 167x and 214x and that this nebula has a pale bluish-greenish colour. This planetary nebula measures 1.5'x 1.2'.Chart No:330,NSOG Vol.2.

2011 August 27th, Saturday

Location:Perdeberg.

Instrument:12-inch Dobsonian Reflector Telescope.

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

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

Seeing:Atmosphere stable with little interference.

Limiting Magnitude:4.9.

NGC 6818

--------

Object Type:Planetary Nebula.

First Impression:This object looks like a planetary nebula.

Time:9:50pm.

Location:Sagittarius.

Chart Number:No.12(Extract taken out of "Atlas of the Night Sky").

Size:9mm Eyepiece:Field Of View:15'/14= 1'.

7mm Eyepiece:Field Of View:15'/13.5= 1.1'.

1.0'+ 1.1'= 2.1'.

2.1'/2= 1'.

Size in Arc Minutes:1'.

Ratio:1:3.

Major Axis:1'.

1'/3= 0.3'.

Minor Axis:0.3'.

Planetary Nebula is 1.0'* 0.3'.

Brightness:Magnitude 9.9.

Brightness Profile:The central nucleus is brighter compared to the far outskirts of this planetary nebula.

Challenge Rating:Difficult.

Description

-----------

This planetary nebula is well shown as a small disk at 167* and 214*.This nebula looks like a smoke ring which is reminescent to the Ring Nebula in Lyra.Although it is much smaller than the Ring Nebula.It is at first a tiny nebula with a miniature doughnut hole.This tiny doughtnut hole of this nebula has a pale green structure and is well defined.

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