The Caldwell Objects

years" and suggests amateurs monitor it in 6inch
or larger telescopes.
When I observed the "Ghost" from Hawaii with
my 4-inch in 1997, five things became apparent.
(1) At 23x the nebula was so condensed that it
appeared simply as a 7th-mag-nitude "star"; only
with intense concentration could I convince
myself that I was seeing a nebula and not a star.
Therefore I believe it is possible to see it with the
unaided eye. (2) At 72x the nebula's central star,
its elliptical inner ring, and hints of its outer halo
are visible if I stare directly at the central region
without using averted vision. (3) The nebula,
with its aquamarine hue, looks more like Uranus
than Jupiter, so it could also be called the Rival of
Uranus. (4) With a quick glance at high power,
d'Arrest's two "nuclei" are readily apparent; they
are the inner rings enhanced extremities. And (5)
with a prolonged glance at high power, Secchi's
inner ring of "stars" can be seen to rotate as the
eye follows those beads of light around.
Amateurs using low power might mistake
the nebula's exceedingly bright inner ring for its
central star. The planetary's high surface
brightness takes magnification well, so be sure to
crank your telescope up to at least 75x for each
inch of its aperture. Direct vision reveals the
central star because it suppresses the amount of
light entering the eye from the nebula; with
averted vision, the entire central ring and the star
blend into one magnificent blur. Do use averted
vision to trace out the full extent of the 45"-wide
outer halo, though. As I mentioned, with a quick
glance at high power the northwestern and
southeastern tips of the elliptical inner ring
shone like two stars. But the longer I looked, the
more sausage-shaped the tips became, until they
split into beads of light; the southeastern
enhancement did so especially well. These are
Secchi's shimmering pearls, the ones that start to
"rotate" as the eye traces out
The Caldwell Objects
59
the ring. Interestingly, Secchi made a similar
observation of the beaded ring in M57, the Ring
Nebula in Lyra; he saw it "glittering like stardust."
Equally interesting is that at 189x, NGC
3242's inner ring was essentially two sausages,
and an increase to 216x showed a fine thread of
light connecting the sausages at either end.
The Ghost of Jupiter is very similar in brightness,
size, and distance to the Ring Nebula. In
true physical terms the Ring spans 0.42 light-year
(27,000 a.u.), while the Ghost measures 0.30 lightyear
(19,000 a.u.) across. Modern studies have
shown that the Ghost's inner ring is an ellipse
inclined some 70° to our line of sight. Most
photographs show a bright and clumpy inner
ring surrounded by a faint, smooth outer
envelope. The Hubble Space Telescope has
revealed a distinct asymmetry to the inner ring,
with the southeastern limb being much brighter
than the northeastern one. The inner ring's inner
edge is scalloped in the Hubble view, and fine
wisps of nebulosity cross the annulus like threads
of finely woven silk. Beyond the nebula's outer
envelope are the mysterious FLIERs (fast lowionization
emission-line regions). These small
knots of material — generally near a planetary
nebula's symmetry axis, on opposite sides of the
central star — have much higher outflow speeds
than the nebula in which they are embedded.
They also generally are much less ionized (that is,
their constituent atoms have retained more of
their electrons). The pale outer halo has a fine
brushstroke quality to it, like the first layer of
watercolor put to a piece of paper. Ground-based
astronomers have also discovered what may be a
dim halo of ionized helium surrounding the
nebula's shell.
NGC 3242's central star may be a triple
system consisting of a white-dwarf star, a very
close brown-dwarf companion, and a more
massive and distant companion. The 0.01-
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