The Caldwell Objects

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object did Caroline discover? Most historians
agree that Herschel simply erred in his endnotes
and duplicated his reference to Η VII-12. If so, Η
VII-13 is probably Η VII-12. This conclusion was
reached by Adm. William Henry Smyth, who, in
his 1844 Cycle of Celestial Objects, wrote of Η VII-
12: " tolerably A compressed but extensive cluster,
on the boundary between the Unicorn, and the
Greater Dog. It was discovered by the
indefatigable Miss Herschel, in 1785."
Once you locate Sirius, look for Caroline's
cluster 3½° due east of 4th-magnitude Gamma
(γ) Canis Majoris, the easternmost star in the
Great Dog's head. Though small, the magni-tude-
7.2 cluster is easily spotted in 7x35 binoculars as a
puff of celestial smoke a little less than ½° east of
a magnitude-5.5 star. Under dark skies even
small binoculars, held with a steady hand, should
start to resolve sections of the cluster. The
magnitude-5.5 star marks the eastern tip of a very
thin, diamond-shaped asterism (3° x 1°) with
Gamma Canis Majoris at the western end; the
diamond's wide southern corner is a fine double
star (magnitudes 6.0 and 6.6) oriented east-west
and separated by some 5'. The diamond points
right to the cluster. If you fail to find NGC 2360
that way, try Smyth's method. He wrote that
NGC 2360 "can be fished up, under a moderately
magnifying eye-piece, at 7°½ [east-northeast] of
Sirius; where an imaginary line from Aldebaran
passed over Bellatrix, will intersect it." (I've put
Smyth's directions from Sirius in brackets,
because his original text erroneously places the
cluster "west-northwest" of the star.) Sharp-eyed
observers under dark skies should challenge
themselves to see NGC 2360 with the unaided
eye. I've tried on some spectacularly clear nights
at an altitude of 4,200 feet and can say only that
the cluster seemed to bob above and below the
very threshold of visibility. My magnitude
estimate (7.0) was made with 10x50 binoculars.
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The view changes dramatically with a telescope.
NGC 2360 is in a fabulously rich star field and
through the Genesis at 23x it appears much as
Smyth describes it, namely "a singular group of
very lucid specks, formed of stars nearly all of
10th magnitude." Most of these "lucid specks"
huddle in a rather elliptical core that has a threedimensional
quality to it; the
stars appear to be piled or stacked on top of one
another in an orderly fashion. With a prolonged
gaze the core starts to look like a butterfly's
beaded chrysalis suspended by silken threads; it's
as if we're about to witness some strange and
wonderful transformation of starlight into star
life. Star-studded arms project from the core to
form a roughly sideways X. A 9th-magnitude star
lies near the tip of the northeastern arm of the X,
between a finely resolved cone of Stardust
extending to the southeast and a jagged trail of
starlight that leads to the northeast. These arms
have faint extensions that loop back in to the
core, so the cluster really does look like a
butterfly in flight. A singular thread of stars
reaches out and nearly touches the 5.5-magnitude
star to the west like a finger about to tap a
shoulder. Ernst Hartung also saw NGC 2360's
concentrated
Deep-Sky Companions: The Caldwell Objects