The Caldwell Objects

Eighth-magnitude NGC 6543 is located about
halfway between the 3rd-magnitude stars Delta
(δ) and Zeta (ζ) Draconis, a mere 10' northwest of
the north ecliptic pole. If you live under dark
skies, you can further refine its location by
placing your finderscope's cross
hairs halfway between the 5th-magnitude stars
Omega (ω) and 36 Draconis. Then, using low
power, look for a slightly bloated "star" just 3'
east-southeast of an 8th-magnitude star. At 23x
through the Genesis refractor the planetary looks
stellar with direct vision, creating the illusion of a
nice 8th-magnitude double star. With averted
vision, though, the planetary swells (the Cat's
Eye winks!), giving away its identity. The nebula
shines with a pale green color even at low power.
As with all plan-etaries, high magnifications give
the best views. In fact, because of their small sizes
and high surface brightnesses, most planetaries
can handle magnifications well beyond those you
might normally consider using on deep-sky
objects. I would recommend using at least 75x per
inch of aperture on an average night.
Alas, little detail can be seen in the Cat's Eye
in the 4-inch, even at high power. The
The Caldwell Objects
planetary's sharp 11th-magnitude central star is
closely bordered by a luminous ring. A tenuous
outer shell of nebulous matter surrounds these
features, giving the planetary a slightly
elongated appearance. Using 450x and a 12-inch
telescope, Christian Luginbuhl and Brian Skiff
note that the "southern end is diffuse while the
northern side has a broken bright edge on the
east and west sides." Of course, detecting fine
structure in any nebula requires excellent seeing.
If you can't resolve much detail in your telescope,
console yourself with this: looking through the
famous 60-inch reflector on Mount Wilson in
California, David A. Allen recorded NGC 6543 as
merely a "pale green uniform nebula" with a
central star. His words magnify the importance
of the Hubble Space Telescope.
The familiar and most conspicuous features
of the Cat's Eye are young, only about 1,000 years
old. In part it is this youthful aspect of planetary
nebulae that excites many amateurs like McNeil.
"In a hobby literally filled with such ages as 4.5
billion years and more," says he, "planetary
nebulae such as NGC 6543 represent events that
are measured on time scales easily grasped
relative to human standards." McNeil also notes
something quite interesting (albeit little known)
about the Cat's Eye. "Part of its 'outer halo' is
actually visible in amateur scopes," McNeil says.
"The object known as IC 4677 is often
miscataloged as a 15.7 magnitude background
galaxy residing less than 2' due west of NGC 6543.
However, further research has overwhelmingly
shown that it is merely a brighter fragment of the
outer halo of the nearby planetary nebula. Such
semi-detached shells of planetary nebulae are
generally extremely faint and difficult to visually
observe. In fact, most exhibit a surface brightness
1,000 to 10,000 times lower than that of the
planetary's
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