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Type: bright nebula
Mag: B=7.44, V=?
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NGC 6888 is a large oval-shaped HII region (Sharpless 105), brightest along its northeastern side. WH's place is close to the knots and streamers on that side of the nebula, and it is clear from his description that that is the part he saw.
Bigourdan puts the position closer to the center of the oval. He descriptions of the field on two nights (he claims to have seen the nebula on only one of them) makes it clear that he did not see WH's object, just two stars near the revised place given in the IC2 notes. It looks like purest coincidence that this is near the center of the HII region.
Synonyms: H IV-072
Discovered in 1792 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a double star of the 8th magnitude, with a faint south-preceding milky ray joining to it, 8' long, 1.5' broad."
"faint, very large, very much elongated, double star attached."
Ced 179 (NGC 6888)
Position (1900): RA 21 8.8, Dec + 38 6
Star: +37 3821 (Mp=6.7, V=7.44, SpT=O6)
Spectrum of nebula: emission spectrum (observed)
Classification: Neb associated with mainly one star (which may be multiple) - star surrounded by a neb envelope with conspicuous structure (eg. IC 5146)
Notes: "NGC 6888 = GC 4561 = H IV 72. Disc. 1792. (93 Pl 43 Pl 44, 114, 208, 216, 366, 550, 578, 615 Pl 21, 630 Pl 16 Pl 17, 631, 715), R. +37 3821 = HD 192163 = Boss 28056."
(Astrophysical Journal Supplement, No 105, 1965) in her Catalogue of Bright Nebulae notes that this nebula is very bright, is more prominent on the red POSS plate and has a maximum size of 20' x 10'.
(Sulentic and Tifft 1973) notes that this is a diffuse nebula.
"WISE morphological study of Wolf-Rayet nebulae" [2015arXiv150306878T]
WR 136: (RA, Dec J2000.0) [20h 12m 06.55s, +38° 21' 17.8"]
Morphological classification: B = WR Bubble. (These nebulae present a thin shell or bubble both in optical and IR, mostly in the W4 band. Examples of these nebulae are those around WR 6 (S 308) and WR 16.)
Distance = 1.26 kpc.
by Jim Lucyk: Astronomy mag. 11/79 p83, Deep Sky #6 Sp84 p25, Deep Sky #7 Su84 p25, Sky&Tel. 5/88 p557, Deep Sky Monthly 8/80 p5, Vehrenberg's Atlas of DS Splendors (3ed) p217, Observer's Guide (Astro Cards) 9-10/87, Vehrenberg's Atlas of Galactic Neb-2 p77, 78.
Notes that through a 10-inch this oval of nebulosity can be seen, and the use of a nebular filter makes the object stand out against the background and suppresses the light from the bright stars in and around the nebulosity.
Harrington, P. (1990) An observer's guide to diffuse nebulae – II. Sky&Telescope, July, 97.
Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "12M; 18' x 12' extent; illuminated by 7M Wolf-Rayet star; like smaller version of N6960 (the "Veil"); use N-filter and low-x; part of the Gamma CYG nebulosity complex; 25' to NE is deep red type-N variable star RS CYG (Period = 417 days; 6.5->9.4M)."
WDS: pair = ADS13515: 7.2,10.6; 13".8; 60.
13cm - 60x: fairly f, sm. inv w/pair of *s plotted on Tirion. vdiffuse area w/convex Nrn perimeter btwn Nrn br * and fntr point E. brtr * is un=pair (7,11; 30"; 65). from this pair thr brtst segment of neb arcs away S, nrly linearly curving W, and is inv w/some f *s. 5Sep1983, USNO.
15cm - nice @ 50x w/UHC; [OIII] not as good. can see complete nebula, brtst W of m7 * nr N end. f twd SE periphery, reaches SE to m10 * in sm grp. annular and essentially blank in center, fades smoothly from ring inward. lots of fld *s sup @ 50x & 80x. BS, 17June1991, Anderson Mesa.
30cm - 125x: long curving and rel narrow arc from pair in pa215 w/sev f *s along its Ern edge. vis for 7' length, < 1' wide. going NE from *, gets wider, lower sfcbr. vf 6'-7' away from pair, then brtns briefly, but fades before reaching * in triangle to E. this part 1'.5 wide. few f *s here, whereas W part has lots. 5Sep1983, USNO.
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