The Caldwell Objects

heart of the cluster, dividing it into two V-shaped
stellar cities before tapering off into a triangular
island of stars. Looking through a 20-inch f/4
reflector at 72x, Wilson notes that the horseshoe's
dark lane is 'Very dark and devoid of stars,
making the cluster appear [weakly] concentrated."
Lining this dark lane like poorly
shielded streetlights are several bright double
stars. Christian Luginbuhl and Brian Skiff note
that many of these doubles are faintly colored.
Two distinct pairs punctuate the ends of the
horseshoe asterism. Higher power in the 4-inch
also brings out an attractive concentration of stars
just south of the eastern pair; the scene looks like
a sparkling mist trapped in a circlet of suns. And
the eastern member of each wide pair is a
telescopic double star with a separation just
under 10".
The Caldwell Objects
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Within 15' of NGC 663's fractured core are 24
irregular variable stars of spectral class Be. These
special stars display bright hydrogen emission
lines superimposed on the normal absorption
spectrum of a hot, B-type star. Be stars are
believed to rotate so rapidly that they shed mass,
forming an expanding shell and a disk around
each star's equator. One of NGC 663's Be stars is
already known as an X-ray source and may be
associated with a neutron star, the result of a
supernova explosion. Future X-ray observations
may enable astronomers to detect other compact
objects in the system. Stepping beyond the
corridors of reality, one can imagine that the
great rift tearing through the cluster's core was
the result of an extraordinary supernova
explosion, one whose supersonic winds pushed
through the crust of stars lining the rift like some
violent volcanic event.
Finally, observers looking for a challenge
might try spotting NGC 654 and NGC 659 in 7x35
binoculars. I did this with difficulty. NGC 654 is
the most difficult, for it is but a breath of haze
slightly offset from a yellowish 7th-magni-tude
star. NGC 659 is also difficult and is distinguishable
from the background Milky Way
only with averted vision. Telescopically, 7.9magnitude
NGC 659 is a small pack of stars — a
C-shaped asterism —within a 5'-wide glow of
partially resolved suns. NGC 654, on the other
hand, is outstanding. The magnitude-6.5 cluster
is tapered, and starlight drips off its tip like water
off a needle. It's such an unusual gathering of
irregularly bright suns that it stands out in the 4inch.
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