The Caldwell Objects

5 9
Ghost of Jupiter; CBS Eye Nebula; Rival of Uranus
NGC 3242
Type: Planetary Nebula
Con: Hydra
RA: 10 h 24 m 46.1 s
Dec: -18° 38' 33"
Mag: 7.8; 7.3 (O'Meara)
Dim: 45" x 36"
Dist: 1,400 light-years
Disc: William Herschel, 1785
W. H ERSCHEL: [Observed 7 February 1785] Beautiful,
brilliant, planetary disk ill denned, but uniformly
bright, the light of the colour of Jupiter. 40" diameter.
Second observation: near Γ diameter by estimation.
(H IV-27)
GC: Remarkable planetary, very bright, little extended toward
position angle 135°, about 32", blue.
M ANY DEEP- SKY OBJECTS LOOK LIKE GHOSTS
in small telescopes, but only one boasts of that
fact in its popular name: NGC 3242, the Ghost of
Jupiter — an object amateurs love to "scare up" at
star parties. In a sense this planetary nebula
really is a ghost. It is a set of translucent gas
shells blown off of a dying sun. The nebula's
shells are expanding outward at speeds of
roughly 30 km per second, and they will continue
to do so until they dissolve into the interstellar
medium like spirits fading from view. You can
see this specter haunting the sky 1.8° southsouthwest
of magnitude-3.8 Mu (μ) Hydrae. Note
that my magnitude estimate for the Ghost of
Jupiter (7.3), made with 7x50 binoculars, is a half
magnitude brighter than the generally accepted
value. So here's your first Ghost of Jupiter
challenge: try to detect the nebula with the
unaided eye. The object is so bright and starlike
that it can be seen with
234
59
NGC: Remarkable planetary, very bright, little extend-
ed toward position angle 147°, 45" diameter, blue.
the eye alone from very dark-sky sites. This
would be a great exercise for those attending the
annual Winter Star Party in the Florida Keys, not
only because Hydra is well placed in the sky on
winter evenings, but also because the star party's
latitude places the nebula higher in the sky than
is the case at midnorthern locales.
Of course, one could argue that all planetary
nebulae are ghostly glows and round like
planets. But NGC 3242 appears about the same
size as Jupiter, so the nickname makes perfect
sense. That being said, there is a misconception
and an enigma associated with the name. In April
1971 the late Walter Scott Houston wrote in Sky &
Telescope that William Herschel discovered the
nebula in 1785, which is true. He also wrote that
"[a]ccording to Admiral [William Henry] Smyth,
'From its size, equable light, and colour, this fine
object
Deep-Sky Companions: The Caldwell Objects