The Caldwell Objects

southern-sky explorer Abbe Nicolas Louis de
Lacaille discovered the Tarantula Nebula from
the Cape of Good Hope in either 1751 or 1752 (no
discovery date was recorded). In his catalog of
southern-sky objects, published in 1755, he writes
simply that the object, when viewed through his
modest ½-inch refractor, "resembles [47
Tucanae], but. . . is fainter." He listed the object
under the heading "nebulae without stars."
Seventy-two years later lohn Herschel described
the nebula as an assemblage of loops, "the centre
of a great spiral." He discussed the Tarantula at
length:
This is one of the most singular and extraordinary
objects which the heavens present, and derives no
small addition to its intrinsic interest from its
situation, which is among the thickest of the nebulae
and clustering groups of the greater Nubecula [the
LMC], of whose total area it occupies one-five
hundredth part. . . . [I]ts real nature has been
completely misunderstood, and its magnified
appearance so strangely misrepresented in the only
figure which I am
aware to have been made of it as to convey an
entirely erroneous impression both of its
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form and structure _____ The stars... scattered
over the area occupied by this nebula may or may not
be systematically connected with it, either as an
individual object, or as part of the vast and complex
system which constitutes the Nubecula. In respect of
their arrangement there is nothing to distinguish
them from those which occupy the rest of the area
covered by the Nubecula, in which every variety of
condensation and mode of distribution is to be met
with. The nebula itself (as seen in the 20-feet
reflector) is of the milky or irresolvable kind — quite
as free from any mottling or incipient stellar
appearance as any other nebula which I can
remember to have examined with that instrument.
The magnitude-8.3 cluster (which is also
embraced by the designation NGC 2070) spans 5'
and contains about 100 suns visible through
small-aperture instruments; its principal member
shines at magnitude 11.8, and most of the others
are in the 12th- to 14th-magnitude range. Some
catalogs list the magnitude of the nebula and the
cluster as 8.3, but this certainly is in error, for that
value pertains only to the cluster.
Through a telescope the Tarantula Nebula
and its associated cluster together stand out as
one of the most profound sights in the night sky.
Apertures of 2 inches and larger will reveal the
object's complex tangle of gaseous loops and
sprays of starlight. A moderate-size amateur
instrument like an 8-inch Schmidt-Casse-grain
will reveal Herschel's assemblage of loops
dramatically. Indeed, the Tarantula's visible
structure rivals its photographic appearance. The
most obvious feature is the nebula's strong
central bar, which extends from north to south
and is centered on 30 Doradus. From it sprawl
several crablike arms and legs, all extending in
seemingly animated ways. A distinct loop, like
The Caldwell Objects 407