The Caldwell Objects

emerge, followed by a diffuse outer halo. The
halo even appears speckled with dim starlight,
but this is an illusion created by Milky Way field
stars. Through the 4-inch at 23x, NGC 2506 is a
small, tight cluster, a knot of stars protruding
from the rich Milky Way background. With
concentration the cluster looks like a dim and
distant globular cluster. The west side of its
dense, asymmetrical core is punctuated by what
appears to be a single sun. The asymmetry favors
the north-northeast, where there is an obvious arc
of stars, many paired.
At 72x the cluster's brightest stars form
loosely spiraling waves of light, with obvious
clumps marking the wave crests; using my
imagination, I see a frothy sea just starting to
churn beneath a waterspout. The star that I
noticed on the cluster's western side at low
power is actually a pair of 11th-magnitude suns.
They sit on the western bank of a V-shaped bay
of relative darkness. Look about 3' east of this
star pair, at the cluster's very core. There you'll
find another fainter and wider pair of stars
anchoring a fuzzy bar of starlight, oriented
north-south, whose northern end fades into a
knifelike point. The cluster's northwestern
section is populated by mean-
The Caldwell Objects
54
dering chains of stellar clumps that lie against a
background haze of unresolved suns. Some of the
clumps make distinct cursive shapes, like the
Greek letters delta (δ), upsilon (υ), and mu (μ).
Some star chains flow like coronal streamers,
especially to the north. At high power, many of
these arms take on a delicate spiral nature. The
southwestern section of the cluster is dominated
by the dark bay, which seems to leak starlight to
the southeast and southwest. Christian
Luginbuhl and Brian Skiff confirm the absence of
starlight in the southern section, writing, "In 25
cm [a 10-inch telescope] the cluster is irregularly
round with a blank spot on the [southern] side."
With a 12-inch telescope they estimated that the
densest portion of the cluster spans about 8' and
shows about 100 stars, most of which are very
faint. At higher powers the cluster's outer
envelope starts to blend in with the Milky Way
background.
Before leaving this region of sky, be sure to
return to NGC 2539 next to 19 Puppis, for it is a
much more pleasing object visually. Also, while
sweeping en route to NGC 2506 I encountered
the 11.6-magnitude galaxy NGC 2525 sandwiched
between two faint stars about 2° northwest
of 19 Puppis.
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