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RA: 06h 39m 10s
Dec: +08° 44′ 11″
Ch: MSA:227, U2:182, SA:12
Type: reflection nebula
Mag: B=?, V=?
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NGC 2261 is often called "Hubble's Variable Nebula" as its variability was indeed first noticed by Hubble during his years at Yerkes Observatory. The nebula was discovered, though, by WH in 1783, and is the second of his new class of "planetary" nebulae. We know now that the nebulosity is actually enveloping a very young double star system, R Monocerotis. The star's variability was first noted by Schmidt (AN 55, 91, 1861). The variability of the nebula is probably the result of circumstellar clouds close to the stars casting shadows on the surrounding nebulosity. NGC 1554 / NGC 1555 (which see) around T Tauri is another example.
Synonyms: H IV-002
Discovered in 1783 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "cB, fan-shaped, about 2' long from the centre."
Lassell, W. (1854) Observations of the nebula of Orion, made at Valletta, with the twenty-foot equatorial. Memoirs R.A.S., 23, 53-62.
"A Catalogue of Estimated Parallaxes of 112 Nebulae, Open clusters and Star Groups", Vol 36 (4), p 107-115.
"star with variable cometic nebula (Hubbles)." He gives the approx. diameter as 2x1 arcmin.
Ced 83 (NGC 2261)
Position (1900): RA 6 33.7, Dec + 8 49
Star: + 8 1427 (variable Mp and V, SpT=Bp)
Spectrum of nebula: continuous and emission spectrum (observed)
Classification: Neb associated with mainly one star (which may be multiple) - Fan-shaped object (eg. IC 59)
Notes: "NGC 2261 = GC 1437 = h 399 = H IV 2. Disc. 1783. WP 30. (114, 174, 209, 216, 217, 294, 298, 359, 360, 361, 431, 450, 451, 452, 455, 457, 458, 459, 482, 486, 491, 509, 515, 578, 619, 631, 690, 693, 694, 791). R. This is Hubble's variable nebula connected with R Monocerotis = +8 1427, varying between the visual limits 9.3-14.0. Reinmuth gives the dimensions of the nebula to be 3.2 x 1.5'."
Duncan, J.C. (1956) Lampland's Study of Hubble's Variable Nebula, NGC 2261. PASP, 68(405), 517-519. [1956PASP...68..517D]
John C. Duncan of Steward Observatory wrote: "This bright little comet-shaped nebula NGC 2261 has been known since the time of Sir William Herschel and was long designated H IV 2, being the second in Class IV ('stars with burs, with milky chevelure, with short rays, remarkable shapes, etc.') in Herschel's Catalogue of One Thousand New Nebulae and Clusters of Stars." In the NGC the object is described as "bright; very much elongated 330 , nucleus cometic = star 11th mag." Duncan notes: "In average-sized telescopes the head of the cometary object appears as a variable star of about the 11th magnitude and, announced as a variable star by Schmidt of Athens in 1861, it was given the designation R Monocerotis. The length of the nebula is about three minutes of arc. In 1916 Hubble, intercomparing photographs made by him with the 24-inch refractor of the Yerkes Observatory and other photographs made by various observers, discovered that the nebula varied in both brightness and in apparent form, and so the object has since been generally referred to as Hubble's Variable Nebula." The star and the nebula vary in brightness from about 10th to 13th magnitude in an irregular cycle. Between 1916 and 1951 the nebula was frequently photographed by C. O. Lampland using the 42-inch reflector of the Lowell Observatory, generating a collection of 940 photographic plates. In John C. Duncan's study of these photographs, he notes: "The object that is called R Monocerotis is not a star but the 'head' of the comet-shaped nebula. It has a hazy appearance, and ... has a narrow spike extending a few seconds of arc southeastward." The nebula was the first object to be photographed with the 200-inch Hale Telescope when it opened on Mount Palomar in 1948.
Lynds, B.T. (1962) Catalogue of dark nebulae. Astrophys.J.Suppl.Ser. 7, 1-52. [also: computer datafile: VII/7A]
The RNGC (Sulentic and Tifft 1973) notes that this is a diffuse nebula.
= N2261, GN 06.36.4.02, Ced 83, Other designations: R Mon
Class: CN (cometary nebula)
Photo Index by Jim Lucyk: Sky&Tel. 2/85 p180, Sky&Tel. 2/81 p117, Sky&Tel. 7/85 p31, Deep Sky #1 Wi82 p6, Burnhams V2 p1203, 1204.
Houston wrote: "Anothern nebula that may be difficult to detect is the faint wisp surrounding R Mon . . Like the star, this small comet-shaped nebula is variable; at times it has been detected with a 3-inch, but at other times it requires a 10-inch . . this object stands magnification well.
MacRobert calls this "an object unique in the sky. NGC 2261 is located 2' southwest of an 11th mag star and has a total mag of about 10. It looks like a little comet with a wide tail. This is a reflection nebula lighted by the variable star R Mon, which is buried in a tiny, bright patch just a few arc seconds across in the nebula's southern tip. The star, or starlike patch, generally remains around 12th mag, NGC 2261 has a high surface brightness as nebulae go, so it shows through light pollution well. 'Quite distinct and easy' I wrote in my notebook using the 6-inch at 110x. I thought I saw irregularities in its east and west sides and a definite westward bend in the tail as it fades toward the north. This is exactly what photographs show. Try using high powers on this object."
Ken Reeves, in "SACNEWS On-line for March 1997", observing with a 10-inch f/4.5 scope, notes: "NGC 2261 (06 39.2 +08 44) This is Hubble's Variable Nebula. At 140x, I saw this as pretty small, pretty bright, fan shaped with the head on the south end. This very much looks like a small comet with a wide tail. The star at the head comes and goes, and averted vision helps extend the tail. This is a very unusual object, hard to describe, and quite a beauty."
Steve Coe (Glendale, Arizona, USA) observing with a 13.1-inch f/5.6 reflector, writes in The Webb Society Nebulae and Clusters Section Report No. 11, January 1993: "At x351, this nebula is bright, pretty large, much elongated and has a much brighter star involved. It appears as a small comet and R Mon is veryu obvious at the tip. The south side is bright and the west side more elongated. At x200,m there are some markings within the nebula. I have inspected this object at high power several times, and believe I have seen changes, but there are differences in seeing, transparency, observing site and telescope from time to time . . . "
Tom Lorenzin, in the electronic version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "10M; 2'x 1' extent; coma-shaped cloud with apex directed SSW; fan-like with vertex angle of 30-35 degrees; at 135x, a hint of structure appears; star at head illuminates the nebula."
Observer: Mark G.Birkmann Your skills: Intermediate (some years) Date/time of observation: 11-4-99 9:00 UT (3:00 am CST) Location of site: New Haven, Missouri (Lat ~38, Elev ~700') Site classification: Rural Sky darkness: 3/4 some high thin clouds 1-10 Scale (10 best) Seeing: 4 1-10 Seeing Scale (10 best) Moon presence: None - moon not in sky Instrument: 40" f/5 dob Magnification: lowest power 125x Filter(s): OIII, H-beta, Orion Ultrablock Object(s): NGC 2261, Hubble's Variable Nebula Category: Reflection nebula. Class: E + R e1 Constellation: Monoceros Data: mag ? size 2' x 1' Position: RA 06h:39m 12s DEC +08 :44' 00"
Description: This nebula appeared to have 3 fairly distinct levels of brightness with the brightest being near the embedded star at the tip. The star did not have a stellar appearance but was embedded in nebulousity. Just behind the star is a small slightly darker lane that is connected to the edge of the nebula and goes about two thirds of the way across. At the back edge of this brightest level nebulousity three features were seen. First, a concave area was noted about one third of the way in from the edge. Adjacent to this was a large dark lane that extended through the middle, dimmer level of nebulousity. An extension of the brightest area of nebulousity went down the side about half way into the middle area of nebulousity. The middle area of nebulousity was fairly uniform in brightness and had a straight rear border that extended to the large dark lane. The border continued on the other side of the dark lane but was a little farther back. The next level of nebulousity was very faint and was only seen on the same side of the nebula as the bright extension into the middle area of nebulousity. I hope to view this nebula again in a few months to look for changes. A drawing can be seen at http://www.fortunecity.com/greenfield/twyford/637/drawings.nebulae.htm
Steve Coe, observing with a 13" f/5.6, notes: "is Hubble's Variable Nebula. Edwin Hubble took many photos of this comet-shaped nebula that show changes in its form. The best explanation is dark masses inside the nebulosity that drift in front of R Mon, the star that illuminates the gas. These drifting dark clouds cast shadows on the glowing gas. There is a set of pictures in Burnham's that show these changes. As a matter of fact, this object is the answer to a good trivia question. It was the first object photographed with the 200" telescope when it was put into operation in 1949. In the 13" at 135X it is bright, pretty large, much elongated and has a much brigher star involved. It appears as a small comet and the star R Mon is very obvious at the tip. The south side is brighter and the west side is more elongated. At 200X there are some dark markings within the nebulosity. I have inspected this object at high power several times and I believe that I have seen changes but there are differences in seeing, transparency, observing site and telescope from time to time. I plan to observe this object over a longer period to see if I can pick out obvious differences when some of the other variables are removed."
[amastro] posting, Sat Nov 25, 2006
82" telescope, McDonald Observatory near Fort Davis, Texas, USA
f/13.7, 35mm Televue Panoptic (5' fov, 812x)
NGC 2261 was another winner, a distinctly fan-shaped nebula radiating away from R Mon. The edges of the fan were sharp but the edge farthest from R Mon just sort of dissolved to nothingness. Immediately north of R Mon there is a finger-like dark nebula that seems to wrap around the star, partially detaching it from the nebula, and making the pointy end of the nebula fairly hook-shaped. A recent Amastro post by Tom Polakis indicates that this dark finger of dust might be a new "variable"...
Observing site: Pinnacles overlook
[6h 39m 12s, 8° 44m 0s] A faint, cone shaped nebula with considerable mottling. It holds magnification well. Lovely.
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.
The shape of this nebula looks somewhat like a fuzzy triangle and this nebula is lit up by areas of very bright light all over.Around the central outskirts of this nebula I have found that its light grows brighter compared to the far outskirts of this nebula.
It measures 1'*0.3'.
The Messier objects
The Bennett objects
The Caldwell list
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