Sky & Telescope - July 2023 - 54

RON BRECHER
JULY 2023 OBSERVING
Suburban Stargazer by Ken Hewitt-White
COATHANGER CLOSE-UP The delightful
Coathanger, first detected with the naked eye,
wasn't logged by legendary observers Charles
Messier or William Herschel. A chance alignment
of 10 stars whose distances range from
237 to 1,132 light-years, the alluring asterism is
worth close inspection in a telescope. The tiny
open cluster NGC 6802, visible in this image,
lies immediately east of the Coathanger.
a 3.2-magnitude orange sun and a
4.7-magnitude blue neighbor 34.9″
away. The colorful components are eyecandy
gorgeous in a wide-angle, 30-mm
eyepiece generating 30× on my 120-mm
refractor. The low magnification tightens
the tandem and includes a generous
amount of surrounding sky. The scope's
panoramic view greatly intensifies the
beauty of the contrasting jewels set
against the glittering Milky Way.
Like the Coathanger, Albireo's
A Cosmic
Coathanger
Caper
A superb binocular target,
the beloved Coathanger also
invites telescopic inspection.
P
oor Vulpecula, the Fox. An inconspicuous
constellation buried in
the summer Milky Way, the sly celestial
fox tries hard not to be seen - and
largely succeeds. Vulpecula contains
no stars brighter than 4th magnitude.
Yet Vulpecula is home to an attractive
group of stars first clearly identified over
a thousand years ago.
The mottled patch of starlight
became known as al-Sufi's cluster, in
honor of Abd al-Rahman al-Sufi, a
Persian astronomer who first noted it
in AD 964. Almost 700 years later, the
Italian astronomer Giovanni Hodierna
independently cataloged the object.
Seattle, Washington amateur Dalmero
54 JULY 2023 * SKY & TELESCOPE
Brocchi prepared a detailed chart of
the intriguing field in the 1920s for
the American Association of Variable
Star Observers - hence the label
Brocchi's Cluster on star atlases. The
cluster graduated to professional status
as Collinder 399 (Cr 399) thanks to a
comprehensive survey of open clusters
that Swedish astronomer Per Collinder
compiled in 1931. Today, stargazers
know it simply as the Coathanger.
Call it what you will, the Coathanger
isn't a true open cluster in which the
stars are gravitationally bound to one
another. Instead, it's an asterism - a
chance alignment of suns lying at vastly
different distances. Even so, Cr 399
is curiously compact and evocatively
shaped. Its 1½°-wide pattern is distinctive
in binoculars and sparkling in
small telescopes. Recently, I explored
the Coathanger and its immediate surroundings
with my 4.7-inch (120-mm)
f/7.5 apochromatic refractor. But any
backyard scope will do, so join me for a
quick Cosmic Coathanger Caper.
Getting There
The famous double star Albireo, or
Beta (β) Cygni, is our gateway to the
Coathanger zone. Albireo features
attractiveness is an accident of alignment.
Measurements by the Gaia
astrometry mission indicate that the
bright orange sun is 60 light-years
closer to Earth than the fainter blue
sun. So, unless contrary evidence comes
to light, Albireo will remain categorized
as an optical double rather than a
physical binary.
The Coathanger resides in southern
Vulpecula, near the border with
Sagitta, the Arrow. How does Albireo
get us there? I have a simple " Anser " to
that. An 8°-long line extended southsouthwestward
from Albireo through
4.5-magnitude Anser, officially Alpha
(α) Vulpeculae, leads directly to Cr 399.
Anser means " the Goose, " a remnant
celestial figure from the late 17th century
when Polish astronomer Johannes
Hevelius declared this area of sky as
" Vulpes cum Ansere " - the Little Fox
with the Goose.
Let's linger on orangey Anser before
moving on to our main target. The star
is an easy catch in any finderscope;
indeed, it's occasionally naked-eye visible
in my gray suburban sky. Nothing
else along the Albireo-to-Coathanger
path is as bright as Anser. Moreover,
Anser is accompanied by a deep-yellow,
5.8-magnitude star 7′ to the northeast.
From that handy combo it's a 4½° hop
to the Coathanger.
Sky & Telescope - July 2023

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