The Caldwell Objects

77
of the nebulous matters between them. There is a very
minute star in the dark space between the preceding
extremities of the nebula: they are extended in the
parallel of the equator nearly.
Several years later John Herschel would call
NGC 5128 "a very problematic object" that "must
be regarded at present to form a genus apart,
since it evidently differs from mere 'double
nebulae,' not only in the singular relation of its
two halves to each other, (having each a well and
an illdefined side, their sharply terminated edges
being turned towards each other and exactly
parallel) but also by the intervention of the
delicate nebulous streak intermediate between
them and lying in exactly the same general
direction."
How bizarre this new nebula must have
seemed to John Herschel, who, like his father,
believed that the Milky Way and all its nebulae
were made up of noth
ing but stars. What was
the dark band that had
seemingly ripped apart
this cloud? In his 1849
'Outlines of Astronomy"
Herschel prophetically
decided that it was a
"similar but much more
strongly marked case of
parallel arrangement
than that noticed by Mr
Bond (in the Andromeda
Nebula) . . . one in which
two semi-ovals of an
elliptically formed
nebula appear cut
asunder and separated
by a broad obscure band
parallel to the larger axis
of the
306
nebula, in the midst of which a faint streak of
light parallel to the sides of the cut appears."
Herschel's reference to George P Bond . was critical,
for Bond had observed in 1847 two parallel
dark "canals" in the Andromeda "Nebula" — one
of the last strongholds of William's Herschel's
nebular theory, which stated that these masses of
nebulous matter were in the process of becoming
new solar systems. By 1888 Isaac Roberts had
successfully photographed the dark lanes in the
Andromeda "Nebula," as did Edward Emerson
Barnard two years later. Soon these features
would be recognized as dust lanes, part of the
visible framework not of spiral nebulae but of
spiral galaxies.
Still, NGC 5128's appearance and nature
remained a mystery. In 1918, Heber D. Curtis
(Lick Observatory) classified it as an "edgewise
spiral with a dark lane." Five-hour exposures
taken of it from Arequipa, Peru, with the
Deep-Sky Companions: The Caldwell Objects