The Caldwell Objects

98 & 99
Dim: 7° x 5°
Dist: 610 light-years and 790 light-years (two overlapping
nebulae)
Disc: Known since antiquity
T HE C OALSACK (CALDWELL 99), A RIVAL OF
Crux though devoid of its splendor, is the Milky
Way's poster child for visual mystery. The
northern tip of the kite-shaped dark nebula lies
due south of the Jewel Box (Caldwell 94), while
its western flank washes against Acrux, the foot
of the Cross. In photographs the Coalsack's size
and shape mimic that of the Cross's interior, so I
like to call it the Shadow of the Cross. Australian
aborigines have probably known of this dark
cloud for more than 40,000 years; it appears, on
tribal bark paintings from Groote Eylandt, as a
speared fish being held up by two brothers over
two fires (the brothers and their fires representing
the four stars of the Cross). Another Australian
legend refers to the Coal-sack as "the
embodiment of evil in the shape of an Emu." The
Polynesians knew it as Te Paniwi a Taewa, a
black fish. And ancient Peruvians perceived it as
the celestial Doe suckling its fawn. In more
modern times the Coal-sack was Amerigo
Vespucci's Il Canopo fosco (the dark Canopus) and
Adm. William Henry Smyth's Black Magellanic
Cloud. In his Oceana, the 19th-century historian
James Anthony Froude called it "the inky spot —
an opening into the awful solitude of unoccupied
space."
Froude's remark reflects William Herschel's
pronouncement that each starless void was a
Loch im Himmel, an opening in the heavens, a
curious vacancy "through which we seem to gaze
into an uninterrupted infinity." In his sweeps of
the night sky, Herschel found a remarkable
coincidence: the blackest voids appeared near the
richest star clusters, which "would almost
authorise a suspicion that the
392
J. H ERSCHEL: None.
GC/NGC: None.
stars, of which it is composed, were collected
from that place, and had left the vacancy." The
elder Herschel specifically cited the black void
near Rho (ρ) Ophiuchi and the globular cluster
M80 as a magnificent example. Had he spied the
Coalsack and its proximity to the Jewel Box —
not to mention the open cluster NGC 4609
(Caldwell 98) within it — his suspicions would
have been magnified.
From South Africa in 1834 Herschel's son,
John, turned his attention to his father's "holes."
At first he presumed them to be "tubular
vacancies" penetrating the depths of space. He
later retracted this view. But scholars like Froude
and authors like Thomas Hardy carried William
Herschel's fantastic view of these voids into the
late 19th century. In his novel Two on a Tower — a
work Hardy created "to set the emotional history
of two infinitesimal lives against the stupendous
background of the stellar universe" — we find
astronomer Swithin St. Cleeve showing the sky
to his imminent lover, Lady Constantine, to
whom he tries to explain the unfathomable size
of the universe:
. . . horrid monsters lie up there waiting to
be discovered by any moderately penetrat-
ing mind ____ Impersonal monsters, namely,
Immensities. Until a person has thought out the stars
and their inter-spaces, he has hardly learnt that there
are things much more terrible than monsters of
shape, namely, monsters of magnitude without
known shape. Such monsters are the voids and waste
places of the sky. Look, for instance, at those pieces of
darkness in the Milky Way.... You see that dark
opening in
Deep-Sky Companions: The Caldwell Objects