The Caldwell Objects

fact, if you look about 7' southwest of S Normae
you will see a wonderful 17'-long trail of seven
suns (ranging from 8th to 11th magnitude and
oriented north-south) that look as if they had
fallen out of one of the imaginary trucks as it
sped away. Immediately south of S Normae is a
tight acute triangle of 9th-magni-tude suns; 5' to
the northwest of S Normae is a near-perfect right
triangle of 10th-magnitude suns; and 5' due east
of S Normae is a stellar rhomboid. The area
immediately surrounding S Normae and the
southern triangle glows with the nagging light of
stars near the limit of visual resolution, and this
background glow continues to the east, tapering
along the way, until it reaches the rhomboid.
With averted vision, this patch has the shape of a
decapitated fish.
At 72x the cluster is a stellar Rorschach test.
Its entire 15' diameter is dappled with at least a
dozen obvious stellar groupings and several
other seemingly nebulous patches that crumble
into stars with any scrutiny. Pale orange S
Normae looks like a nova at the tip of a tiny
Sagitta-like asterism. (Note that S Normae is not
centered in my drawing because, when I was at
the eyepiece, the greatest concentration of stars
seemed to lie to the south of that star.) The
southern end of this arrow is a fine double star; it
marks the southeastern corner of the acute
triangle I saw at low power. Some 5' southeast of
S Normae lies a small circlet of about a dozen
dim suns — one of those nebulous patches that
crumble into stars when examined with averted
vision. In part it looks nebulous because at least
three of its constituent stars are close pairs. Those
of you with moderate- to large-sized telescopes
should use high power on this circlet and see if
you
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can't "discover" a roughly 13th-magnitude double
on its western edge. A really nice double lies 5'
east of S Normae in the rhomboid. And the
northern star in that pair is an even closer double
that should be scrutinized at high power. These
descriptions of doubles could go on forever. The
field is littered with them. And it's really futile
for me to say what geometric patterns you'll see
beyond those I've mentioned, because these are
only the obvious ones (to me, anyway).
If you happen to have a visitor at your
telescope when you're looking at NGC 6087,
share with him or her the fact that each arcminute
of cluster spans about 1 light-year (9.5
trillion km) in space. That should enable your
companion to fathom the astounding vastness of
our Milky Way.
Planetary nebulae are extremely rare in open
clusters. NGC 2818 in Pyxis is the only open
cluster known to contain one. Other apparent
pairings, such as that of the cluster M46 and the
nebula NGC 2438, are coincidental alignments of
objects at different distances. So you can imagine
the excitement Detlev Koester (Louisiana State
University) and his colleagues must have felt
when they discovered a previously unknown
planetary nebula in the field of NGC 6087 (its
equinox 2000.0 coordinates are R.A.16 h 19 m 16 s ,
Dec. -57° 58' 25"). Alas, in a 1989 issue of
Astronomy and Astrophysics they concluded that
the cluster and the nebula are not physically
associated. PN G327.7-05.5, the 19th-magnitude
planetary, is 28,000 light-years distant — nearly
nine times farther away from us than the cluster.
The planetary spans 14.2", which translates into a
shell of gas nearly 2 light-years in diameter. Now
there's a wonderful challenge for you CCD users.
The Caldwell Objects 353