The Caldwell Objects

NGC 6231). Under averted vision the cluster
appears to lie in the foreground of a galactic mist,
an illusion caused by the faint glow of
unresolved suns, many of which belong to the
rich Milky Way background. Use high power and
averted vision, and faint suns will peek out from
the dark crevices between the brighter suns. If the
arrowhead seems to visually sag to the east, it's
because that's the densest part of the cluster, with
a miniature assortment of some half dozen suns.
Under high magnification many of the stars
appear to be paired. The
two brightest suns marking the weapon's northern
corner are themselves fine doubles; the
northernmost of these two pairs shines at magnitude
5.5 with a 7th-magnitude companion 65"
away at a position angle of 13°.
The cluster's radiance is magnified with even
a slight increase in aperture. Through a 6-inch
telescope Christian B. Luginbuhl and
76
Brian A. Skiff recorded 100 stars (not all cluster
members) in a 10' area, and they saw many blue
stars and small geometric patterns at low power.
James Dunlop, who used a 9-inch reflector, saw a
"cluster of pretty bright stars of mixt small
magnitudes, considerably congregated to the
centre, about 10' diameter, with a large branch of
very small stars extended on the north side."
With a 12-inch telescope Ernst Hartung spied
"many bright white and yellow stars, and many
pairs and triplets, which sparkle in patterns of
lines and small groups." And with
her 13.1-inch f/4.5 reflector
Barbara Wilson recorded
"eight brilliant white stars
with dozens of fainter
members in a very
nebulous region" at the
1986 Texas Star Party; the
cluster's center, she noted,
"has [a] dimmer streamer
curving around it and a
smaller streamer [to the]
south."
Do not stop with
NGC 6231. The entire
region is worth exploring.
Certainly there is nothing
like it in the entire sky for
small-telescope users. Just
north and east of the
cluster, out to about 3°,
are three open clusters
(Trumpler 24, NGC 6242, and NGC 6268), a
planetary nebula (IC 4637), a diffuse nebula (IC
4628), double stars, colored stars, Milky Way
patches, and a swath of dark nebulosity
(Barnard 48). It's a cornucopia of celestial riches.
IC 4628 lies at the northeastern end of Trumpler
24, 1½° northeast of NGC 6231. It is an irregular
90' x 60' patch of faintly glowing
The Caldwell Objects 303