The Caldwell Objects

98 & 99
Allan Poe's horrifying Pit, where "the blackness
of darkness" supervenes and all sensations
appear "swallowed up in a mad rushing descent
as of the soul into Hades." It is the bleak black
heart of the Milky Way. I first saw the Coalsack
in 1982 from the cockpit of an Air New Zealand
Boeing 747 flying south at an altitude of 40,000
feet. From that darkened cabin the Coalsack
needed no introduction. Through the thin highaltitude
air it looked like an immense pool of
haunting darkness and misty vapors, a black fog
hugging the foot of the Cross — the antithesis of
Dante's four principal virtues (see Caldwell 94,
page 376). The Coalsack was by no means the
blackest cloud I'd seen, but the Milky Way in this
region is so intensely bright that the enormous
dark nebula stood out immediately. The object's
size (7° x 5°) also called to mind Smyth's Black
Magellanic Cloud. Not only are the Coalsack and
the Large Magellanic Cloud roughly the same
angular size; the Coalsack is about as
conspicuous against the bright Milky Way as the
Large Magellanic Cloud is against the relatively
dark skies of Dorado and Mensa. It's unfortunate
that the brightest objects in the heavens have
been given negative magnitude numbers; if it
were otherwise, we could create a "negative
brightness" scale for dark nebulae. For example,
since the Large Magellanic Cloud shines at
magnitude +0.4, the Coalsack's "dark magnitude"
could've been -0.4. It wouldn't have been a
perfect scale, but it would have given observers
some idea of these objects' visibility.
The Coalsack has a magical quality to it, and
its appearance can change suddenly and eerily
under averted vision. I observed it one evening
from the nearly 14,000-foot-high summit of
Mauna Kea. My 7x35 binoculars revealed a vast
smoky clot, a blotch of negative space, an erased
section of the Milky Way. Closer
examination showed the dark nebula's main body
to be square and sharply ribbed. Through the 4inch
at 23x these ribs were thin trails of black
smoke, which made me wonder if dark nebulae
had anything to do with the ancient notion that
stars were flames. Bill Harby, the editor of Island
Scene magazine, was with me that night, and he
compared the Coalsack to black ice with a
multitude of streamers. Indeed, under a relaxed
gaze the cloud transforms into a series of black
satin veils seemingly frayed by age. One
prominent veil starts immediately southeast of
Acrux, where you'll
find a conspicuous ink spot with two parallel tails
of darkness flowing to the east. The northernmost
of these tails passes just south of the sole nakedeye
star in the Coalsack, the Retype variable BZ
Crucis, whose light fluctuates subtly around
magnitude 5.2. Another prominent veil marks the
sharp northernmost border of the Coalsack, just
south of the lewel Box. And an isolated black
puddle forms the southern "tip" of the kiteshaped
nebula. Seeing this
394 Deep-Sky Companions: The Caldwell Objects