Sky & Telescope - September 2021 - 40

Summer Observing
with them is 61 Cygni, or Piazzi's Flying Star. It's named
after the Italian astronomer who first noticed the star's
unusual habit of not sitting still in the sky. Arguably one of
the most interesting stars in the heavens, 61 Cygni is both a
true double and a high-proper-motion star, meaning that it's
moving quickly across the sky. " Quickly " in this case means
5″ per year, or roughly 1° every 720 years. To put it another
way, it takes about eight years for Piazzi's star to move one
Jupiter diameter. Its rapid apparent motion is partly due to its
proximity - only 11.4 light-years away. Most double stars are
too distant to split with handheld binoculars, but 61 Cygni is
near enough that it's worth a shot. With a current separation
of 31.8″, this pair is a bit tighter than Albireo, whose colorful
components are 34.6″ apart. I find I need at least 15× to crack
61 Cygni's 5.2- and 6.0-magnitude stars.
Faintly Familiar
As you shift your gaze from the Swan's eastern wing back to
Deneb, you may encounter a vast field of nebulosity with a
familiar shape. This is the North America Nebula, NGC 7000
- an immense emission nebula that looks remarkably like its
namesake. At my favorite camping area near the Salton Sea in
California, the nebula is visible to the naked eye and shows
considerable detail in binoculars. In particular, look for the
embayment on the southwestern side (in the sky!) that corresponds
to the Gulf of Mexico. If skies are exceptionally clear
and dark, you may also detect a glowing patch floating where
the Atlantic Ocean should be. That's the Pelican Nebula, IC
5070. It's a much tougher catch thanks to its lower surface
brightness and the presence of a couple of bright foreground
stars competing for attention.
About 9° northeast of Deneb is M39, the best binocular
open cluster of the tour. Whereas many of the other clusters
I've mentioned are too small or faint to offer much resolution,
even 7× binos will show M39 to be a roughly triangular
arrangement of 6th- to 8th-magnitude stars. A scattering
of lesser lights adds to the cluster's glow and helps pull it
out from the surrounding star field. Photographs show the
blue-white stars of M39 set against a background of predominantly
yellow field stars. I've yet to detect these colors
in binoculars, but M39 is pretty and complex enough that I
return to it often.
The final stop of our tour is worth exploring with binoculars,
but it may be best appreciated without optics. Look
for a dark patch of sky between the North America Nebula
and Sadr. This is the Northern Coalsack, a particularly
dense knot of interstellar dust in the plane of the Milky Way.
Broaden your view to encompass the whole galactic band, and
you'll see the Coalsack as the start of a dark slash that cuts
through the bright star fields of the Cygnus Milky Way, paralleling
the spine of the Swan. That dark river is part of the
famous Great Rift, which runs southward toward the galactic
center in Sagittarius. The Great Rift isn't a hole in the Milky
Way but rather one of the dust lanes that clot the spiral arms
of our galaxy.
Cygnus is so rich that just
Selected Binocular Targets in Cygnus
Object
Type
Albireo
NGC 6871
NGC 6883
Biur 2
NGC 6910
Cr 419
M29
IC 1318
NGC 6819
NGC 6826
Double star
Open cluster
Open cluster
Open cluster
Open cluster
Open cluster
Open cluster
Emission nebula
Open cluster
Planetary nebula
Veil Nebula Supernova remnant
NGC 7063
61 Cyg
NGC 7000
IC 5070
M39
Open cluster
Double star
Emission nebula
Emission nebula
Open cluster
Mag(v)
3.2, 4.7
5.2
8.0
6.3
7.4
7.6
6.6
-
7.3
8.8
-
7.0
5.2, 6.0
5.0
8.0
4.6
Size/Sep
34.6″
30′
35′
12′
10′
5′
10′
50′ × 30′
5′
36′
2.9°
9′
31.8″
120′ × 100′
60′ × 50′
31′
RA
19h 30.7m
20h 06.5m
20h 11.3m
20h 09.2m
20h 23.2m
20h 18.1m
20h 24.1m
20h 22.2m
19h 41.3m
19h 44.8m
20h 51m
21h 24.2m
21h 06.9m
20h 59.3m
20h 51.0m
21h 31.9m
Dec.
+27° 58′
+35° 47′
+35° 51′
+35° 29′
+40° 47′
+40° 44′
+38° 30′
+40° 15′
+40° 11′
+50° 32′
+30° 48′
+36° 29′
+38° 45′
+44° 31′
+44° 24′
+48° 26′
Angular sizes and separations are from recent catalogs. Visually, an object's size is often smaller than the cataloged
value and varies according to the aperture and magnification of the viewing instrument. Right ascension and
declination are for equinox 2000.0.
when I think I've seen it all,
I'll stumble across a previously
overlooked cluster, asterism, or
beautiful double star. For this
tour I've only described a handful
of the constellation's best
and brightest objects. Cygnus
will reward a more patient
exploration - its open clusters
alone could keep a determined
observer busy for a whole
season. But do yourself a favor
and set the binoculars down
occasionally to appreciate how
much of the grand structure of
our home galaxy can be seen
with your eyes alone. We're
part of that picture - soaring
through the Milky Way along
with Cygnus. And we have so
much to explore.
¢ Contributing Editor MATHEW
WEDEL has been writing this
magazine's Binocular Highlight
column since June 2016.
40 SEPTEMBER 2021 * SKY & TELESCOPE

Sky & Telescope - September 2021

Table of Contents for the Digital Edition of Sky & Telescope - September 2021