AK
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FU
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skyandtelescope.com • SEPTEMBER 2019 55
nestled against an 11.5-magnitude
secondary to the northeast. With my
10-inch scope at 43×, I saw this same
concentration of stars near the center
of a larger and brighter collection with
an 8th-magnitude star at its western
edge. This makes the cluster about 20′
across, embracing 50 mixed bright and
faint stars.
William Herschel obviously cata-
loged the bigger group. The Catalogue
of Open Cluster Data (2004) lists NGC
6793 as being 18′ across with a 7′ core,
so it seems that references giving a size
of 7′ limit the cluster to the stars of the
more highly condensed core.
Collinder 399 is a striking asterism
commonly known as Brocchi’s Clus-
ter or the Coathanger. It has several
stars bright enough to be seen with the
unaided eye in a very dark sky. From
my semi-rural home in upstate New
York, I merely see a nebulous haze 4½°
south of Alpha. Binoculars or a fi nder
show six stars in a curved bar plus four
more forming a hook to the south.
Since the bar is 1.4° across, seeing the
Coathanger in a telescope requires a
low-power, wide-angle fi eld of view.
Stephan Ruchhöft from northern
Germany reads Sky & Telescope’s Ger-
man edition, Astronomie Heute [Editor’s
note: no longer in print]. Stephan wrote
telling me that he “discovered” Col-
linder 399 while scanning the sky with
binoculars. At the time he was planning
a family trip to the Alps, which inspired
him to see the star fi gure as a ski lift.
The bar of the Coathanger is the ski
lift’s cable, and the hook is its chair.
This inventive image has the advan-
tage over the Coathanger of being seen
right-side up in binoculars by Northern
Hemisphere observers.
Just 18′ off the eastern end of the
Coathanger’s bar, we come to the open
cluster NGC 6802. My little refractor
at 28× displays a broad, north-south
band of mist about 5′ tall. A pair of
9th- and 10th-magnitude stars lies
6½′ northwest, and another pair of
10th and 11th magnitude lies the same
distance northeast. A smattering of
extremely faint stars dots the haze at
87 ×. With my 10-inch refl ector at 170×,6802Stock 1(^68306823)
6800
6793
LDN 810
Σ 2548
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7
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VULPECULA
CYGNUS
Cr 399
(Brocchi’s
Cluster)
19 h 50 m 19 h 40 m 19 h 30 m 19 h 20 m
+28°
+26°
+24°
+22°
S +20°
ta
r^ m
ag
ni
tu
de
s^2
3 4 5 6 7 8
Deneb
Vega
Altair
On September evenings
the prominent Summer
Triangle, comprising the
stellar beacons Vega,
Deneb, and Altair, spar-
kles amid the Milky Way’s
glow. In the accompany-
ing text, Sue French tours
deep-sky objects near
the center of this wide-
fi eld photograph.