Astronomy

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Shining only 0.3 magnitude fainter than M29,
NGC 6811, sometimes called the Smoke Ring
Cluster, lies almost 2° northwest of Delta Cygni
and is one of the Swan’s overlooked treats. When
Danish amateur astronomer Tommy Christensen
used a 3.5-inch refractor to view the cluster in
the mid-1980s, he thought it was one of the most
beautiful he’d ever seen, likening it to a smoke
ring of stars. The cluster has about 250 members
scattered across 15' of sky. The hole is a contrast
illusion created by a ring of brighter stars around
a cloud of fainter sparklers.
NGC 6866, occasionally called the Frigate
Bird Cluster, is another obscure but fanciful open
cluster. You’ll find this Caroline Herschel discov-
ery about 3½° east-southeast of Delta Cygni.
NGC 6866 has a small bulbous protrusion to
the north, punctuated by a brilliant yellow star
that marks the tip of the bird’s powerful beak.
This pouch of stars is followed to the south by an
ellipse of stars from which extend two long wings
of starlight — one to the east, one to the west. A
zigzagging line of stars to the south marks the
bird’s tail. If you sweep across this area at 60x
with direct, then averted vision, see if the bird’s
pouch doesn’t puff in and out, breathing life into
this celestial creature.

Hiding out
NGC 6946 is a spiral galaxy seen nearly face-on.
It features a pair of branching arms that have a
puzzling propensity for supernova explosions,
with nine known to date — thus its moniker, the
Fireworks Galaxy. Shining at 9th magnitude,
NGC 6946 is among the closest galaxies to the
Local Group, hiding out in the far northeastern
corner of Cygnus, only 2° southwest of Eta (η)
Cephei and just ⅔° from open cluster NGC 6939
in Cepheus.
We end our tour of Cygnus with Cygnus X-1
(R.A. 19h58.4m, Dec. 35°12', epoch J2000.0),
one of the best known black hole candidates.
Although we cannot see the black hole —
the brightest X-ray source detected in Cygnus
— we can see through the smallest of telescopes
HDE 226868, its 9th-magnitude blue supergiant
companion on which the black hole feeds. It’s a
fun and thought-provoking target.
From large emission nebulae to tiny
black holes, Cygnus is a wonderland of light
and shadow, harboring some of the most
fascinating — and strangest — objects known.
Enjoy it during your summertime observing
nights, returning to these objects until they
become old friends.

Stephen James O’Meara is a veteran deep-sky
observer, author of numerous books on astronomy,
and columnist for Astronomy magazine.

The beautiful face-on

galaxy NGC 6946 is one of

Cygnus’ greatest deep-sky

treats. TONY HALLAS

Ye t an ot h e r o b s c u r e

but beautiful open cluster

is NGC 6866, a sea of

suns almost lost in the

rich Cygnus Milky Way.

MARTIN C. GERMANO

The bright

bluish-green star in the

center of this image is HDE

226868, the supergiant star

feeding the celebrated

black hole Cygnus X-1.

ANTHONY AYIOMAMITIS