The Caldwell Objects

not be found in planetary nebulae, which have
nothing to do with planets or their formation.
NGC 2392's true grandeur surfaced with the
advent of photography. Photographic plates —
especially those taken with large telescopes in red
or ultraviolet light — show the nebula's
concentric shells primped with fine details. The
central star lies at the core of a bizarre gyroscopic
arrangement of bright gas, which in turn is
surrounded by an annular fanfare of radial
streaks. Such a sight compels our eyes to search
for patterns, just as they would in the body and
folds of a cloud in tumult. Once ignited, our
imagination transforms the nebulous patches into
something fanciful, like a face. Indeed, NGC
2392's most popular nickname is the Eskimo
Nebula because of the way it resembles a face
peering out from a fur-lined parka. Ultravioletlight
photographs tend to exaggerate
the "nose" (the planetary's hot
central star), thus the nebula's
other popular nickname, the
Clown-Face. Of course, we see
what our own imaginations
dictate. In his Celestial Handbook
Robert Burnham Jr. says the
"whole nebula irresistibly
suggests the classic and
unforgettable features" of the
late comedian W C. . Fields. I
have called NGC 2392 the Lion
Nebula ever since childhood, for
to me the pattern most
resembles the face of a cartoon
lion whose large and bristling
mane surrounds its smiling
countenance.
Imagination aside, what i s
NGC 2392, really? Planetary
nebulae once were believed
The Caldwell Objects
39
to be the abruptly ejected atmospheres of massive
red-giant stars. However, this simple theory
could not account for the wild shapes seen in
these objects. There is a veritable zoo of heavenly
creatures among the planetaries, including
silkworms, butterflies, and eggs wrapped in
kudzu. In the late 1970s, Sun Kwok (now at the
University of Calgary, Canada) and his
colleagues conceived of a new theory of
planetary-nebula formation. They started with a
red-giant star sloughing off its outer atmosphere
and exposing a white-hot core (a white-dwarf
star in the making). They then envisioned
superfast winds streaming out from the hot
central star and compressing and accelerating the
slower circumstellar material that was ejected
earlier; the interacting winds would create the
shell shapes we see in planetaries today. Kwok's
theory was vindicated when the
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