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NGC 7009
Saturn Nebula
PK037-34.01
RA 21:04:12
Dec -10° 49.5'
Planetary
nebula |
Discovered on September 7, 1782 by William
Herschel (H IV-001) with an 18.7-inch f/13 speculum telescope. He called it "vB,
nearly round, planetary not well defined disk." He observed it in 1784 with
his newly completed 18.7-inch f/13 (20 feet) speculum telescope. He wrote: "I
have examined it with the powers of 71, 227, 278, 460 and 932; and it follows
the laws of magnifying, so that its body is no illusion of light. It is a
little oval, and in the 7-feet reflector pretty well defined, but not sharp on
the eges. In the 20-feet it is much better defined and has much of a planetary
appearance, being all over of an uniform brightness, in which it differs from
nebulae: its light seems however to be of the starry nature, which suffers not
nearly so much as the planetary disks are known to do, when much magnified."
The NGC records it as "a magnificent
object, very bright, small and elliptic." Lord Rosse coined its popular
name, Saturn, after the extending rays, or ansae, which project from the main
disc on either side.
In the 5th edition of Webb's Celestial Objects
for Common Telescopes it is described as "planetary: somewhat elliptic:
very bright for an object of this nature: pale blue; not well defined in
5.5-foot achromatic, but bearing magnifying more like a planet than a common
nebula. One of the finest specimens of these extraordinary bodies . . . E. of
Rosse finds a very thin ray on each side, which I saw with Huggin's 15-inch
achromatic. Lassell detects within it a bright well-defined elliptic ring.
Buffham, 9-inch speculum, an opening. Se., who made its diameters 25 and 17
arcseconds, saw it sparklem and thought it a heap of stars."
Burnham notes that this nebula was one of the
first observed by Lord Rosse with his 6-foot reflector, and is described in his
1850 paper "Observations on the Nebulae". Rosse saw the nebula as a
fairly uniform luminous disc, reports Burnham, but Rosse was apparently unable
to detect the darker centre or the central star. In Rosse's words: "It has
ansae which probably indicate a surrounding nebulous ring seen edgeways."
Burnham
calls the Saturn a "strikingly beautiful object in large telescopes."
He notes that it shines with a "vivid green fluorescent glow" and
calls attention to the conciderable intricate detail in both rings, and notes
that the two projecting rays end in bright condensations about 44" apart.
Hartung notes that a 30cm shows an even light,
the faint rays only visible on very clear nights. The nebula is elliptical,
about 20x15 arcsec in pa 70 degrees, and no nucleus visible.
Walter Scott Houston has seen the central star
using the 20" refractor at Van Vleck Observatory in Connecticut, but could
not see it with his 10-inch reflector. He recommends using high powers to dim
the planetary itself, thus accentuating the star. Houston calls this nebula "one
of the brightest planetaries in the heavens, and its oval 8th mag disk is easy
to spot with small telescopes. ... to see NGC 7009's extensions, or ansae,
you'll generally need a 10- or 12-inch telescope. Although I have never seen
them in the 4-inch Clark refractor, I glimpsed them with a 4-inch off-axis
reflector. I've received reports from amateurs noting the colour of the Saturn
nebula as light green, bluish green and bright blue. After a cataract operation
.. I see it as brilliant blue, while the other eye - its lens yellowing with age
- sees it as deep green."
Listed by the Herschel Club, described as “has
a blue tint, shows some elongation, large and opaque. 8-inch, 96x.”
Mullaney writes: "This 8th mag blue-green
egg is a planetary measuring 44 arcseconds by 26 arcseconds. Its name comes
from two very faint thin extensions best seen in photographs. Visible only in
large amateur telescopes, they are reminiscent of Saturn with its rings seen
nearly edge on. The planetary's intense disk has an eerie cast to it, making it
a fascinating sight in even the smallest of telescopes. After Herschel found
this one (the first of his class IV discoveries) it's easy to see why he pressed
on for more!"
Darren Bushnall (Hartlepool, Cleveland)
observing with a 8.5-inch f/6, writes in the The Webb Society Nebulae and
Clusters Section Report No. 11, January 1993: "Visible as a small,
elongated, very blue disc at low power. At x180, the two projections showed
themselves as small spikes in PA 80 and 260 degrees. Nebular diameter about
35x16 arcseconds."
Phil Harrington (1990, Touring the Universe
through Binoculars) says that it is "visible in binoculars as a greenish
point of light and is famous for having one of the highest surface brightnesses
of any planetary."
John Bortle (Webb Society Quarterly Journal,
January 1976) using 10x50 binoculars, estimates the visual magnitude as 7.8.
James B. Kaler ("The Amateur Scientist",
Scientific American, May 1992) notes: "Through an 8-inch, Beryl Cadle saw
'a bright bluish , oval nebula, hazy around the edges.' Using a 20-inch,
Barbara Wilson observed its ansae and its double-shell structure ... No one,
incidentally, saw the central star itself."
Tom Lorenzin, in the e-version of "1000+
The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: “8M;
25' x 15' extent; bright, blue-green ellipse with detail visible at high-x with
N-filter; faint "Ansae" extend E-W; radial brightness non-uniform.”
Steve Coe, using a 17.5” f/4.5, notes: “is
the Saturn Nebula, a famous planetary with outer ansae (wing-like projections)
and a bright inner disk. It was discovered by William Herschel in 1782 but Lord
Rosse was the first to see the extending ansae. The projections reminded him of
the planet Saturn and he gave this object its' nickname. Amateurs have been
trying to duplicate that observation ever since. Using the 13" at Cherry
Rd. on a 8/10 night; Bright, pretty large, elongated 1.5 X 1 in PA 75, at 220X
the central star and ansae are obvious and the nebula is light green. This
observation of the Saturn Nebula is made with Helen and Richard Lines' 20"
f/6 Newtonian in Meyer, Az. The nebula is bright, small, somewhat elongated and
light green at 150X. Raising the power to 225X will show the ansae as faint
projections from the bright central section. At 400X the central star is obvious
and the ansae stand out more clearly. One of the bright spots along the ansae
(Helen Lines calls them wing tanks) is visible at this higher power. All these
observations are on a night I rated 7/10 for seeing and transparency and I found
that the UHC filter did NOT help with either the central disk or the ansae
detail. Several observers, myself included saw the nebula as light green,
without the UHC filter installed.”
The catalogued size is 25', integrated
magnitude 8.3 and the VorontsovVelyaminov description reads "ring structure".
The RNGC (Sulentic and Tifft 1973) notes that this is a 8.5 mag planetary
nebula. Terzian Y (1980) Q.J. R.astr.Soc vol 21, p82-92 [09.16.1] notes that
this planetary shows multiple shell structure, possibly having a triple shell.
11x80: Seen as a small star,
as it sets behind Stellenbosch mountain. But wow - two totally different objects
in reality. (suburban skies, seeing 7, transparency 7, sky darkness 6, lim.mag.
at south pole 6.0 (naked eye), 10.7 (binoculars at pole), strong SE wind) [AS]
Meade 8 inch, Super wide-angle 18mm
eyepiece; 36' fov: Large, bright elliptical, pale blue planetary
nebula, getting much brighter to the middle. Standing out beautiful against the
background with a multitude of stars in the field. Maybe a bit uneven structure?
[MS]
8 inch f/7 Newtonian, 66x:
Small and very bright; uniform brightness. Looks like a dim unfocussed star.
Slightly oval in the east-west direction. [GG] |
