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RA: 00h 47m 3.3383s
Dec: −11° 52′ 18.923″
Ch: MSA:316, U2:261, SA:10
Type: planetary nebula
Mag: B=11.43, V=11.78
Synonyms: H V-025
Discovered in 1785 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "four or five pL stars forming a trapezium of about 5' diameter. The enclosed space is filled up with faintly terminated milky nebulosity. The stars seem to have no connexion with the nebulosity."
This planetary nebula in Cetus is recorded in the NGC as "very faint, large, four stars in diffuse nebula."
"! F, R, 4' in diameter, with well-defined edge. Described as spiral by Isaac Roberts but it is more like the Owl nebula. The three stars involved seem to be surrounded by dark spaces and are thus probably connected with it."
Planetary. Confirms description in HOB 9 but five stars are shown to be involved in the nebula.
Knox Shaw, H. (1915) Note on the nebulae and star clusters shown on the Franklin-Adams plates. M.N.R.A.S., 76(2), 105-107.
Comments on papers by Harding (MNRAS, 74(8)), and Melotte (MemRAS 60(5)) describing objects foundon the Franklin-Adams plates; compares with plates taken with the Reynolds reflector (Helwan Obs Bull. 9-15):
NGC 246 is not a spiral, but like the Owl nebula.
by Jim Lucyk: Sky&Tel. 4/70 p221, Sky&Tel. 6/75 p402, Sky&Tel. 6/86 p632, Astronomy mag. 10/84 p78, Astronomy mag. 10/86 p40, Deep Sky #6 Sp84 p15, Burnhams V1 p651, Burnhams V2 p1175, Vehrenberg's Atlas of DS Splendors (3ed) p19.
Q.J. R.astr.Soc vol 21, p82-92 [09.16.1] notes that the central star of this planetary is a visual binary.
The RNGC (Sulentic and Tifft 1973) notes that this is a planetary nebula.
Burnham calls it "very faint, large, slightly elongated, 8.5 mag, 4' x 3.5', with 12th mag central star."
Observer: Jeff Medkeff; Your skills: Advanced (many years); Date/time of observation: ; Location of site: Rockland Observatory, Sierra Vista, Arizona (Lat +31.5, Elev 4550 ft.); Site classification: Rural; Sky darkness: 6 Limiting magnitude; Seeing: 6 1-10 Seeing Scale (10 best); Moon presence: None - moon not in sky; Instrument: 4.5" f/7 Dob; Magnification: 32 53 68; Description:
NGC 246 pn in Cetus; not too dim, 3 stars superimposed? At first I thought this was an O/C. Large. No sign of nearby NGC 255 (=not seen). [See Burnham's p. 651 for a photo that illustrates why I mistook this for a cluster at first glance. The nebulosity is full of mottling, and there are 4 superimposed stars, 3 of which I could see more or less clearly. Observation on another night showed the object rather easier; the mottling was evident, as were the stars, and overall the nebula gave a strong impression of a small, scattered, partially resolved open cluster, even though I knew better.]
Hartung calls it "a rather faint luminous ring 2' across internally, pale bluish and fainter in the following region. There is a faint central star, and two others involved. A faint object with a four-inch telescope."
Sanford calls it one of his favourite objects, describing it as a "fairly large round planetary nebula containing three stars of about the same brightness, one of which is the central star. There is a dark spot near the centre which can be seen with large amateur telescopes. An oxygen or deep sky filter helps show the faint disk against the sky background." The galaxy NGC 255 lies 15' to the north-northeast.
Listed by the Herschel Club, described as "very large and difficult to observe. Oval in shape, opaque with 3 field stars situated near the planetary. A 6th mag star 3' east, forms a triangle south of phi 1 and 2 Ceti. 8-inch, 48x."
William P. Clarke (San Diego, California, USA) writes in The Webb Society Nebulae and Clusters Section Report No. 10, July 1992: "Large, round, dim patch of nebulosity with four stars inside, one near the centre. The central area is less bright than the outer. the outer edge is well-defined. (21-inch f/20, x140)."
Houston notes that the total light output of this nebula is about 8 or 9th mag. The surface brightness is low because the light is spread out over an area about 4' across. Houston notes that with averted vision he could see it in a 4-inch refractor. He writes that it lies "About 6° north of Beta Ceti . . . measuring 4' x 3.5', this planetary has a low surface brightness . . . I was just able to detect it in a 6-inch refractor, although I knew exactly what to look for. There are several stars scattered in front of it, and one must ignore them. Lack of any central condensation makes the object still more difficult."
Tom Lorenzin, in the electronic version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes "11M; 4'x 3.5' extent; faint but large; has 12M center star and 12.5M star 2' due S of center; 12.5M star on ENE edge; SP GAL N255 (12M; 3' diameter) 20' to NNE."
Steve Coe, using a 13" f/5.6, notes: "is a very nice planetary to break up all these galaxies. It is bright, large and round at 100X. There are several dark areas in this nebula and they combine to look like this is a doughnut someone took a bite from. The UHC filter makes this effect more noticeable. There are three stars involved at 165X. 13" Sentinel 8/10 150X bright, pretty large, irregularly round, bright rim at edge, looks like donut with bite missing, adding the UHC filter makes it more prominent, not bigger, but helps the contrast very much."
Marling, J.B. (1986) In pursuit of planetaries. Sky&Telescope, Jun, 631.
Observer: Yann POTHIER (France) Your skill: advanced (many years) Object: NGC 246 (PK 118-74.1; PN G118.8-74.7; ARO 43) Category: planetary nebula Constellation: CET Object data: Vmag=10.9; Bmag=8.0; 240"x210"; type IIIb; central star of Vmag=11.95; discovered by W. Herschel in 1785; ELCAT: [OIII, 496+501nm] = 5 x [Hbeta, 486nm]. RA/DE: 00h47.00m, -11°53.' (2000.0) Date and UT of observation: 02 August 1995, 02h20UT Location & latitude: La Clapiere Obs. (France, latN44 40 00, longE06 27 36) Site classification: rural, alt.1650m (5500ft) Limiting magnitude (visual in UMi): 6.31 with averted vision 10% of the time Transparency (1 to 5 - best to worst): 1 Seeing (1 to 5 - best to worst): 2 Moon up (phase?): no Instrument: Coulter 445mm/17.5" F/4.5 Magnification: 312x Filters used: OIII, UHC
Description: at 312x and OIII filter, large and bright PN, round about 4.1' (246") in diameter, or, more accurately, slightly oval (246x222") along a NW-SE axis, the edges are very sharp; the PN is clearly annular from the E (PA90°) to the SSE (PA165°) going through N and W sides (3/4 of the entire circle); a small and very faint crescent of nebulosity seems to miss from the E and S sides (from PA90° to PA165°); the thickness of the ring is varying between 40 and 60"; the central star of mag11 is in the center, another 2 of mag11 are 1.0'WSW (PA240°) on the disc and 2.3'NW (PA325°) just against the border; one last star of mag14 stands in the "faint crescent" region, 1.6'ESE (PA115°); a kind of dark globule (diam.50") stands against the central star to the NE; another dark globule more elongated (50"x40" in PA150°/330°) stands to the W of the SW (from central star) mag11 star, but farther from its star-companion compared to the first one; UHC and OIII both provides good contrast gain on this object; I suspected the central star's companion as a mag15 star appearing as an elongation from the central's glare towards SSW (PA210°).
Note: the low OIII/Hbeta ratio, typical of low excitation PNs (as for NGC 40, but less extreme case).
Observer: Yann POTHIER (France) Your skill: advanced (many years) Object: NGC 246 (PK 118-74.1; PN G118.8-74.7; ARO 43) Category: planetary nebula Constellation: CET Object data: Vmag=10.9; Bmag=8.0; 240"x210"; type IIIb; central star of Vmag=11.95 (with Vmag=14.28 companion at 4"); discovered by W. Herschel in 1785; ELCAT: [OIII, 496+501nm] = 5 x [Hbeta, 486nm]. RA/DE: 00h47.00m, -11°53.' (2000.0) Date and UT of observation: 02 August 1995, 02h20UT Location & latitude: Chateau-Renard Obs. (France, latN44 39, longE06 28) Site classification: mountain peak, alt.2950m (8900ft) Limiting magnitude (visual in UMi): 6.3 with averted vision Transparency (1 to 5 - best to worst): 1 Seeing (1 to 5 - best to worst): 3 Moon up (phase?): no Instrument: Cassegrain 24.4"/620mm F/15 Magnification: 900x Filters used: none
Description: at 900x, faint and irregular ring but the purpose was to find the central star's companion and it was accomplished at this power: the faint star was separated from the main mag11 star but I did not recorded the PA...
Note: double central star of Vmag=11.95+14.28 at 4" (to PA210°, SSW?).
Observer: Yann POTHIER (France) Your skill: advanced (many years) Object: NGC 246 (PK 118-74.1; PN G118.8-74.7; ARO 43) Category: planetary nebula Constellation: CET Object data: Vmag=10.9; Bmag=8.0; 240"x210"; type IIIb; central star of Vmag=11.95; discovered by W. Herschel in 1785; ELCAT: [OIII, 496+501nm] = 5 x [Hbeta, 486nm]. RA/DE: 00h47.00m, -11°53.' (2000.0) Date and UT of observation: 27 July 1990, Location & latitude: La Clapiere Obs. (France, latN44 40 00, longE06 27 36) Site classification: rural, alt.1650m (5500ft) Limiting magnitude (visual in UMi): - Transparency (1 to 5 - best to worst): 1 Seeing (1 to 5 - best to worst): 2 Moon up (phase?): no Instrument: Meade SCT 8" (203mm), F/10 Magnification: 45-145x Filters used: UHC
Description: at 45x, 2 stars on a quite round nebula; at 80x, better seen with averted vision, 2 centrals stars and another on one side and 2 more outside the disk; at 145x, with UHC, 3 "quasi-central" stars in triangle, in a well visible homogeneous nebula.
Note: the low OIII/Hbeta ratio, typical of low excitation PNs (as for NGC 40, but less extreme case).
See also "Visual Astronomy of the Deep Sky" by Roger N. Clark (1990, Sky Publishing Corporation) page 72.
POSS: star 2 56" SW
star 3 2'.15 NW at very edge of neb
star 4 1'.46 SE (m13)
star 5 2'.8 SW off neb
star 6 4'.0 SSE
Landolt: cen * V=11.78/-0.29
15cm - found easily @ lox. medium power shows three *s inv in vf neb.
- mod br but rel losfcbr neb w/four *s inv @ 50x and fifth off to S. all filters helpful at this Dec, [OIII] esp so. 80x shows it best: circ glow wkning twd center, outline missing in SE sector. cen * is brtst of six in or close to neb: second is immed SW well w/in neb; next at very edge on NW; fourth m13.5 SE well w/in neb; fifth just outside on SW; sixth well off to S. [OIII] shows thin outer rind veasily, fading to diffuse border on SE. annularity wk but clr. BS, 29Sep1989, Anderson Mesa.
25cm - vf. three *s about m10.5. indef patch of neb 3' diam. not impressive. [neither is this observation]
30cm - grp of five *s in crude `?' pattern. suspect middle * is cen *. three Nrn *s appear sl nebulous.
[amastro] posting, Sat Nov 25, 2006
82" telescope, McDonald Observatory near Fort Davis, Texas, USA
f/13.7, 35mm Televue Panoptic (5' fov, 812x)
Completely fills the field of view at 812X, large ring around the outside with a fairly ragged edge. Double star in the center, I suppose one of them is the CS.
Karoo Star Party, Britstown, Northern Cape, ZA.
15x70 Celestron binoculars.
Large but faint, round glow, its light evenly distributed, gives this galaxy [nebula] a remarkable soft appearance. Easy to find in binocular field of bright stars; two stars northward (phi-1 and phi-2 Cet) help secure its position as the southern tip of an equilateral triangle.
11/10/1993: Observing with a 6-inch f/8.6 Newtonian, 52x shows it easily as an irregular nebulous patch, large, containing three small stars forming a long isoceles triangle (this triangle points to a 7-8th mag field star, which is itself part of a large almost equilateral triangle). Definitely saw it in hand-held 11x80's after careful study, only using averted vision, as a pretty large, misty, round patch. On this night, 5th mag Nu Cet was easy with the naked eye (alt approx. 45°).
This is a most interesting object; in a 10-inch f/5 at 30x it looks like a faint nebulous open cluster involving a few reasonably bright stars. Higher powers (120x) don't really help to make it look like a planetary; I see an elongated triangle of three equally bright stars. This triangle appears to be involved in faint nebulosity. On the opposite side of the triangle are three fainter stars, which add to the impression of an open cluster.
1997 October 28, Tue/Wed: Jonkershoek, seeing 3, transparency 3, sky darkness 4, lim.mag. at south pole 6.0 (naked eye), 10.7 (binoculars). 11x80 tripod-mounted. "A 90 arcsec, round, very faint haze; readily seen once found."
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.
Object Type:Planetary Nebula.
First Impression:This object looks like a planetary nebula.
Chart Number:No.8(Extract taken out of "Atlas of the Night Sky").
Overall Shape:At 214 magnification this planetary nebula's annular shape is easily seen.This planetary nebula is well defined.
Brightness Profile:Right from the centre of this planetary nebula it grows slightly bright.
Challenge Rating:Very Easy to observe in aperture sized telescopes from 12-inch onwards.
Is a disk seen? No.
Is the edge sharply defined? No.
What colour is the nebula? In the UhC filter this nebula appears whitish in colour, while in the OIII filter this nebula has a reddish cast and at the same time,more details is seen as a large cloud of faint gas and dust that is left over.
Is there a central star? In the middle of this planetary nebula a hot central star together with two other stars illuminate this planetary nebula.
Observing site: Little Tycho Observatory
[0h 47m 0s, -11° 53' 0"] A faint, large, planetary nebula. I did not see the circular outline as seen in its photos. Rather, it appears as5 faint stars enveloped with nebulosity.
Observing site: Little Tycho Observatory
[0h 47m 0s, -11° 53' 0"] Perhaps seen. Extremely low contrast, if so.
The Messier objects
The Bennett objects
The Caldwell list
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