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NGC 3242
Ben 45
Ghost of Jupiter
PK261+32.01
RA 10:24:47
Dec
-18° 37.6'
Planetary nebula
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This remarkable planetary in Hydra is known as
the Ghost of Jupiter, after a comment on its appearance by Admiral Smythe. It
was discovered by William Herschel (H IV-027) on February 7, 1785 with his newly
completed 18.7-inch f/13 speculum telescope. He called it "a beautiful,
very brilliant globe of light; a little hazy on the edges, but the haziness goes
off very suddenly, so as not to exceed the 20th part of the diameter, which I
suppose to be from 30 to 40 arcseconds. It is round, or perhaps a very little
elliptical, and all over of an uniform brightness: I suppose the intensity of
its light to be equal to that of a star of the 9th magnitude." and also as "Beautiful,
brilliant, planetary disk, ill defined, but uniformly bright, the light of the
colour of Jupiter. 40 arcseconds diameter. Second observation, near 1' diameter
by estimation."
h: "a very fine, large, planetary nebula,
25 arcseconds in diameter; a little elliptic; very bright; uniform, but owing to
a hot wind too ill defined for detailed examination." On the next sweep, he
saw it as "planetary nebula, or a decided pale blue colour, but not so full
a blue as the planetary nebula [NGC 3918] ; oval; pos of the longer axis = 135
degrees approx.; 30 arcseconds long; 25 arcseconds broad; uniform and very
bright; but not quite sharp at the edges." On a third occasion he called it
"very bright, decidedly elliptic, a little dim at edges; colour very
decided pale blue; diam in RA = 3s. Pos of longer axis about 130 degrees; pos of
the nearer of two companion stars = 172 degrees." His final observation was
"viewed past meridian; place from Piazzis' Catalogue. Somewhat hazy, with a
slight nebulous atmosphere. Colour a decided blue; at all events a good
sky-blue. Elliptic; pos of axis = 140 degrees; diam in RA 2.5s. Has 2 companion
stars (a) pos = 173 deg. (b) pos = 137.8 deg." He sketched this and other
planetary nebulae, commenting: "[these] represent planetary nebulae, a
class of special interest, and of which, considering their general rarity, the
southern heavens have afforded a rather unexpectedly large harvest. Those only
are here delineatted which have either accompanying stars, or which are
distinguished by some peculiarity, as ... [NGC 3242] which has a slight
chevelure or nebulous haze exterior to its large oval disc; ..."
Hartung notes: "Photos indicate a central
star 11.3 mag in a broad spindle 26 x 16 arcsec in pa 145 deg which lies in a
fainter ellipse 40 x 35 arcsec. I have made out these features with 30cm, the
spindle being brightest at the ends."
Houston notes that a 6-inch scope will show a
bright central region as well as traces of a fainter outer envelope. "In my
5-inch moonwatch scope it is bright and easy . . since the surrounding field is
poor, this planetary is quite eyecatching. It is ringlike, with a surface
brightness only three times less than M57 . . I have used up to 150x on NGC 3242
without image breakdown. Under good conditions a 6-inch scope shows the 11th mag
central star."
Texereau and Sagot, in Revue des
Constellations, write: "Easily visible, starlike in a 27mm 13x finder.
Readily recognized as a planetary of appreciable size and with shaded edges in a
55mm refractor at 50x. Central part uniform and very bright in a 95mm refractor
at 95x. Elliptical in a 200mm reflector at 200x. Central part grayish, and
squared into a bright lozenge with a dimming outer edge, in a 215mm reflector at
375x. Colour bluish or yellow."
Steve Coe, observing with a 17.5" f/4.5
at 100X, notes: " Wow, Looks like CBS eye, greenish at all powers, Central
star easy at 300X. Very bright, large, round. AT 650X on a night I rated 8/10
for seeing, there is a small, dark circular area around the central star. A very
nice planetary with lots of internal detail at high power. Sentinel 13"
8/10--100X bright, pretty large, little elongated 1.2 X 1 PA 135, central star
comes and goes with the seeing, light green or aqua. 220X--CBS eye obvious dark
background and bright oval that encompassed the central star. Still very light
green. UHC makes the central star disappear. 440X--Best view, several bright
knots to southeast of central star, bright spots within CBS oval. High power
shows the color as grey, not green, but high power brings out most detail,
including central star and bright knots in disk.
Tom Lorenzin, in the electronic version of "1000+
The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "8.9M;
40" diameter; large, bright and round; 11.5M center star visible at 285x;
annular bright ring apparent midway from center to outer edge; a.k.a. the "Cat's
Eye"."
IAAC contribution by Chuck Layton: (8-inch f/6
Newtonian): This nebula is a small to medium sized planetary that is fairly easy
to distinquish from surrounding stars at low powers. It was a vivid blueish
green at 76X. The central bright area was slightly triangular in shape with a
small darker "lane" visible on the SE side extending outward from the
center. In addition a slightly mottled edge was noticed with averted vision on
the W to SW edge of the brighter center. A dimmer outer halo was uneven in
brightness with a brighter, denser portion on the N side. The halo was elongated
a bit to the SE. The central star was not visible. This planetary is fun to
observe because of all the minute and subtle details. A very captivating object.
I probably spent over an hour describing, sketching and just plain admiring the
thing. All this excitement, I'm sure, is due to the 2 hour sucker hole that
opened up at midnight!!! I've had just about enough of El Nino this year,
thanks!
Mullaney calls it a "truly stunning pale
blue planetary in Hydra .. this 9th magnitude object is as least 40 arcseconds
by 35 arcseconds in extent. Visible in a 60mm refractor at 70x, it rivals the
famous Ring nebula, M57, yet is unknown to many observers. The nucleus has shown
strange variations over the years and should be monitored in 6-inch or larger
telescopes."
William P. Clarke (San Diego, California, USA)
writes in the The Webb Society Nebulae and Clusters Section Report No. 11,
January 1993: "A bright football-shaped structure with a darker centre
containing the central star. A fainter, circular halo gives the nebula the
appearance of an eye, or the CBS logo. The football-shaped part is elongated in
PA 125 degrees and the overall diameter is 0.75'. The central star is obscured
through the OIII filter, while the rest of the nebula is greatly enhanced.
(21-inch f/20, x350)"
IAAC contribution by Adam Albino: Round,
bright, with soft iridescent blue green glow. No real "ring" formation
seen. Solid "ball" Structure. Skiff and Luginbuhl see some brightening
on the NW side as well as some elongation (oval)in shape. I did not see this
with the 8", although at higher powers I felt the edges were not as sharp.
Interestingly I felt that the Mag. of the object was much higher then stated -
easily 7.5. Very nice break from all those faint Fuzzy galaxys nearby!
Donald J. Ware: This is a very impressive
planetary nebula, showing a blue-green disk almost 1' in diameter with a bright
center and fuzzy edges. I saw a bright spot on the SE edge, and another but
fainter brightening to its NW."
While Smythe called it "pale
greyish-white" in colour, Houston notes that many modern observers see it
as striking blue; Hartung does not mention colour.
10-inch f/5 Newtonian: This
planetary is clearly visible in a 10-inch f/5 at 30x, appearing as a bright
bloated star; no matter how you try, you cannot focus it into a point. The
starfield around it is pretty busy, containing bright and faint stars. I was
surprised to see that it would be so large at 30x. However, even with the 10mm
eyepiece, about 120x, the planetary does not show too well in this instrument
tonight. 10mm shows it as a large, pale disc, slightly elongated. The right eye
shows it pale washed-out yellow, while it may have a bluish tinge with the left
eye. When the numerous field stars are brought sharply into focus, the planetary
still has a nebulous border, remaining fuzzy and not sharply terminated. [AS]
13.1-inch f/4.4 Newtonian: “This
object is readily seen with 37x. At 151x it is very big (45’’ x 60’’)
and bright. At first, it seems circular and with defined borders. Careful
investigation shows that it is slightly oval n the WNW-ESE direction; the
southern border is more defined than the opposite one. Its brightness is not
totally uniform; it has a brighter part to the east of the centre. There are a
few stars in the field of NGC 3242.” [9.7mm S.Plossl, 151x, 21’ fov,
sketched] (urban) [GG]
15.5-inch f/9 Newtonian:
Observers used to hunting planetary nebulae will find this object most
impressive and a relief from the usual "stellar" or "stellar with
faint outer envelope" descriptions. With an angular diameter larger than
Saturn's, no "special tricks" are needed to see this object. Observing
conditions, however, greatly influence the appearance of the nebula. At 220x it
appears essentially void of structural detail, except for a fainter ridge which
surrounds the brighter central elongated mass. This central disc appears
featureless, although the Northern tip shows a slight brightening. No prominent
colour was noted. [AS] |
