The Caldwell Objects

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3324. This section of the Eta Carinae complex is a
virtual five-car train of clusters and glowing
hydrogen gas.
Now return to the head of the teardrop and study
it carefully. It is bisected by two crisscrossing
dust lanes. The darker of these two lanes runs
from the teardrop's southeastern rim and curves
northeastward to the west of orange Eta Carinae.
In photographs this lane is a black S-shaped
ribbon of opacity, with a dark black knob at its
northern end and a bell-shaped bottom. These
intensely dark segments resemble a keyhole,
which is why it is referred to as the Keyhole
Nebula. (Remember that "Keyhole" refers to a
tiny black smudge within the bright nebula, and
not to the bright nebula itself.) Try as I might,
with the 4-inch I could not distinguish the
keyhole within this lane of darkness. Another
fainter lane of darkness courses east-west
through the teardrop just south of Eta Carinae. It
does not show well in long-exposure
photographs but is very apparent at the eyepiece.
Of course, when we look at Eta Carinae we
are not seeing the star itself but the expanding
gas lobes — the aforementioned Homunculus.
Enrique Gaviola invoked the term in a 1950
Astrophysical Journal article, saying the lobes
looked like a mannequin or homunculus,
complete with "head pointing northwest, legs
opposite and arms folded over a fat body." These
globs of nebulosity should be monitored very
carefully. (It's amazing we can see them at all!) In
the first edition of his Astronomical Objects for
Southern Telescopes, Ernst Hartung writes that
"bright orange η Car is surrounded by an orange
red nebula about 3" wide, just visible with a [4inch],
and the spectrum of the star shows
numerous bands with the red Η α shining like a
tiny lamp at one end." With my 4-inch I could not
see the famed Homunculus as distinctly as
Hartung did with his, but Eta
Carinae was brighter when I was observing, so
the star's increased brilliance conceivably could
have made this delicate feature less distinct. To
me Eta Carinae looked like two slightly
overlapping orange spots. In 1982 New Zealand
amateur Graham Blow took me to the 9-inch
refractor at Carter Observatory in Wellington to
view Eta Carinae, and it was there that I observed
the Homunculus for the first time with amazing
clarity. Through that scope the Homunculus
looked like two puffs of glowing orange light 1"
on either side of an intense core of light. Tom
Clark, the editor of Amateur Astronomy magazine,
described the Homunculus as two balloons
covered with kudzu after seeing it through a 25inch
reflector that he took from Florida to
Australia.
A massive, dark checkmark separates the
brighter, cometlike northern section of the
nebula's heart from its dimmer, more rectangular
southern section. Allen notes that this vacancy
was called the "Crooked Billet" by Francis
Abbott. The southern section is a dense 20'-long
aggregation of sparkling starlight immersed in a
smooth cotton coffin of glowing gas. The coffin is
oriented north-south and contains the scattered
"bones" of Collinder 228, a magnitude-4.4 cluster
with an indeterminate number of stars. Collinder
228's dominant stars are strung out like a
skeleton's groping hand and forearm. The hand,
with strings of stars radiating like outstretched
fingers, is to the north, while the starlit arm lies
to the south.
Thus run the Eta Carinae Nebula's brightest
components. Its second tier of nebulosity swirls
like four butterfly wings, with the densest to the
south. These features are delicate, and in fact
they are better seen in binoculars, where their
light remains condensed, than in a telescope. The
faintest third tier is an even more delicate fan of
gas extending from the northern "comet" to the
northwest and north-
368 Deep-Sky Companions: The Caldwell Objects