The Caldwell Objects

the object was known to some civilizations but
not others.
Herschel wrote that it "would manifestly be
impossible by verbal description to give any just
idea of the capricious forms and irregular
gradations of light affected by the different
branches and appendages of this nebula." But I'll
try. My first view of the Eta Carinae Nebula was
with the naked eye in February 1982, while flying
at 40,000 feet (12 km) to New Zealand. The
nebula was a magnificent presence, not the eyesquinting
cough of light that some sources imply.
And that's the way it looks now from Hawaii. Its
bright northern section was so intense in
February 1998 that I saw it in diminishing
twilight with the unaided eye. And in twilight,
with 7x35 binoculars, the object looked like a
wedge-shaped asterism of two separate star
clusters surrounded by gas. In fact, on the face of
it my twilight view must've been very similar to
Lacaille's dark-sky view with a vaguely
comparable instrument. In the twilight another
object, open cluster NGC 3293, is visible, about 2°
to the north-northwest of Eta Carinae, as a
compressed 5th-mag-
92
nitude glow. (Strictly
speaking, NGC 3293
comprises both clustered
stars and nebulosity, but
only the former stood
out in the twilight.) As
darkness fell, more and
more of the Eta Carinae
Nebula appeared in
patches, until its bright
central chrysalis of stars
and gas emerged as a
celestial butterfly with
impressively broad
wings.
At 23x in the 4-inch
the Eta Carinae Nebula
displays three tiers of intensity. Its brightest
material, which is centrally located, comprises
two concentrations of light. The brighter of these
two, the northern one, is teardrop-shaped. The
teardrop's head contains two open star clusters:
10'-wide Trumpler 16 (with ten stars, including
Eta Carinae) and 5'-wide Trumpler 14 (with five
stars), 10' to the north. The nebulosity
surrounding these clusters tapers to the
northwest, where, 45' away, it beads up again at
the 14'-wide cluster vdB-Ha 99, a loose but rich
aggregation of suns collected around a 5thmagnitude
star. (For brevity this modest cluster
is labeled "vdB" in the chart above.) A narrow
vapor trail streams away from vdB-Ha 99 to the
northwest, like a comet's thin ion tail. In fact, this
brighter northern section reminds me of the
remarkable Comet Hyakutake (C/1996 B2). The
tip of the tail points to NGC 3324, a bright patch
of irregular nebulosity that surrounds a star
cluster and the 9th-magnitude double star h 4338
(6" separation; east-west orientation). And the
cluster NGC 3293 (which has its own overlapping
nebulosity) lies ½° north-northwest of NGC
The Caldwell Objects 367