The Caldwell Objects

perfection than is actually the case; it is shown as
a perfect nebulous miniature of Saturn." Not
surprisingly, Rosse dubbed it the Saturn Nebula.
(Arguably it should be called the Ghost of Saturn
Nebula to parallel Caldwell 59, the Ghost of
Jupiter Nebula in Hydra.)
Equally fascinating is Adm. William Henry
Smyth's 1836 impression of NGC 7009 as seen
through his 6-inch refractor: "This object is bright
to the very disc, and but for its pale blue tint,
would be a very miniature of Venus." (Thus my
other suggested name, the Venus Nebula.)
Herschel, and later Smyth, believed planetaries to
be solar systems in formation, and one can sense
the excitement engendered by this belief in the
remainder of Smyth's description:
If this object be only equally distant from us with the
stars, its real dimensions must be such as would fill the
whole orbit of Uranus. Now a globular body of the
magnitude of the orbit of Uranus, would contain
within its periphery more than 68,000 millions of
globes as large as our Sun!
One can only imagine what Smyth would
have penned had he seen a photograph of this
extremely bizarre planetary taken with a large
telescope. In such photographs the
nebula is a ghostly array of nebulous
rings and baubles, a pendant of celestial
jewels strung together by diaphanous
vapors. At the core of this gaseous locket
is an aged sun's nearly naked heart.
Unlike the central stars of many
planetaries, NGC 7009's is fairly easy to
see in small telescopes. It shines at
magnitude 11.5 and resides in the hollow
of a bright elliptical ring inclined 84°
from our line of sight. That ring has a
sharply defined exterior and a scalloped
interior, which together suggest the
"lips" of a smiling clamshell - especially
since the northern and
The Caldwell Objects
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southern boundaries of the ring are brighter than
its eastern and western extremities. A fainter,
elliptical ring surrounds the bright inner ring,
and it is adorned with a mysterious alignment of
bright knots and condensations along its northern
and southern edges. Most enigmatic, however,
are the two evanescent rays protruding eastnortheast
and west-southwest from the nebula.
Each ends at a bright knot or bead.
NGC 7009's progenitor was probably a mainsequence
star of about 2 solar masses. It is now a
hot, bluish dwarf with a surface temperature of
about 55,000° Kelvin. Strong ultraviolet radiation
from the central star causes the nebula to
fluoresce. To most eyes the nebula glows with a
blue or green tint, the visual signature of doubly
ionized oxygen atoms. The hot central star's
rotation may have caused the irregularities along
the inner edge of the inner ellipse. Actually, the
inner nebula contains two rings of material,
probably related to different episodes of mass
ejections. The rings are not aligned. This may be
due to the central star precessing, its rotational
axis wobbling about once every 30,000 years. An
unseen companion object could be driving this
precession; if so,
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