The Caldwell Objects

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viewing to binoculars. As Walter Scott Houston
once said, "[the] apparent size of Omega Centauri
depends not only on the size of your telescope
but also on your reaction to seeing scattered light.
It's rather like the better-understood 'cocktailparty
effect' — the more sensitive you are to
hearing, the more conversations you will
overhear." Under averted vision Omega Centauri
grows faint radial arms that project against a halo
of teasingly faint suns.
At 23x in the 4-inch the cluster looks like a
snowball illuminated from the inside. The eastwest
trending core seethes with glowing globs of
melded starlight. Two hazy beams stretch to the
northeast and southwest, respectively (the
northeastern one being the more prominent),
while claws of stars jut out from the southern rim
of the core. A 9th-magnitude star burns about 4'
north of the loose and visually serene center.
Omega Centauri's core lacks the intense central
concentration of light that its rival 47 Tucanae
displays; its texture is softer, recalling salt piled
onto a wad of cotton. When the cluster is high in
the sky, use low power to
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look for color. I see a slight yellow tinge to the
core while the outer halo has a pale blue luster.
Increasing the magnification to 72x transforms
the cluster into a web of gossamer threads
surrounding a sizzling skillet of starlight. Look
for a pair of 12th-magnitude suns directly at the
center of the core, which is bordered by east-west
trending arcs of stars to the south. At high power
the globular dissolves into innumerable beads of
quicksilver. The
northernmost section of the inner
core has a dark and prominent
keyhole or "footprint" stamped on it.
(I put "footprint" in quotes because
the feature was first pointed out to
me by an anonymous observer in
the darkness of a Texas Star Party.
This also may be the "hole" John
Herschel noted in his description on
page 318.) Running from the northnorthwest
to the south-southeast,
this footprint lies on the eastern side
of a ribbed wedge of stars; look for
several thin "comet tails" of fuzzy
starlight jutting northeastward from
the easternmost rib. The densest
part of the cluster core is
asymmetrical. It lies on a bed of fainter suns that
scintillate in the background like stellar static. A
long curving lane of darkness sweeps though the
southern half of the dense core like a big smile;
its southern levee is lined with stellar filigree.
Undulating waves of stars flow away from this
black wall to the south. All kinds of clumps,
stellar strings, and dark patches scar the
globular's face. The arms on the western side are
more flamboyantly curled, while those on the
eastern side form long wisps that gradually
decrease in intensity, like fading smoke trails
from skyrockets. Visions of evaporating ice
chips, crystal flames, and light-snapping
Deep-Sky Companions: The Caldwell Objects