46 ASTRONOMY • OCTOBER 2019
W REGION 2
Our journey into Region 2 begins with
a visual punch: beautiful Albireo, twin
jewel of the north. This 3rd-magnitude
golden gem has a 5th-magnitude
emerald-blue companion 34" to the
northeast. Visual astronomers have
adored it ever since they first turned their
telescopes to it.
Sweeping 2½ ̊ north-northeast of
Albireo, we encounter a hidden 9th-
magnitude wonder: Campbell’s
Hydrogen Star. So tiny (5") and compact
is this planetary nebula that it appears
virtually stellar until you boost the mag-
nification to 200x and beyond. At its core
is another treat — HD 184738, an 11th-
magnitude [WC] star — a rare Sun-like
star that recently ejected much of its
original mass and continues to lose mass
at a high rate.
Once again we return to Delta Cygni,
but hop 3½ ̊ east-southeast to another
Caroline Herschel discovery: the Frigate
Bird Cluster (NGC 6866). Shining at
magnitude 7.5, this dynamic stellar aggre-
gation displays about 130 stars of 10th
magnitude or fainter across 16' of sky.
Splayed out in avian form (like its name-
sake), this long-tailed celestial “bird” even
has a throat pouch of glittering stars.
Now look 3 ̊ to the north-northeast of
NGC 6866 to 4th-magnitude Omicron^1
Cygni, which has a 5th-magnitude line-
of-sight companion 5.6' to the northwest,
making a great naked-eye test. But only
1.2 ̊ southwest of ο^1 lies another small
(7.5") planetary nebula that glows at 11th
magnitude. In a 3-inch refractor, it
requires high magnifications to perceive
its pale blue disk well; try 225x.
We now turn our attention about 8 ̊
north-northeast of Deneb (Alpha Cygni)
to the “other” coalsack of Cygnus, Le
Gentil 3. Near the northern shore of this
5 ̊-wide black lagoon we find the delight-
ful Coatbutton Nebula (NGC 7008). At
low power, the 10th-magnitude planetary
nebula looks like a wide (100") skirt of
light dangling from a 9th-magnitude
star. Use moderate magnification to spy
its dark eyes at the core, which makes
the nebula look like a button sewed onto
the velvet sky.
Continuing our northeastward trek,
we come to the stunning 4th-magnitude
star Mu (μ) Cephei, otherwise known as
Herschel’s Garnet star — one of the most
brilliant of all the red giants and arguably
the reddest star visible to unaided eyes.
Less than 1½ ̊ south and slightly west is
the 4th-magnitude Misty Clover Cluster
(Trumpler 37) and its associated emission
nebula IC 1396 (170' x 140'), which
together form the core of the Cepheus
OB2 Association. This celestial delight
has one more prize: 5.5-magnitude
Struve 2816, a striking triple star system
at the center of Tr 37. All the components
reveal themselves admirably at 72x.
Our next treasure, Delta Cephei, is
most popularly known as the prototype
of the Cepheid class of variable star.
But it’s also a neglected double star of
unsung glory, consisting of a yellow pri-
mary (magnitude 3.5 to 4.4) and a 6th-
magnitude green companion 41" distant
— a beautiful sight through any telescope.
The Wizard Nebula (NGC 7380) and its
associated open cluster lie just 2 ̊ to the
east. Yet another Caroline Herschel dis-
covery, this appears as a “coarselyscattered” array of stars in a patchy
cocoon of fragmented nebulosity, filigreed
with veins of dark nebulosity. It’s also a
roughly 3 million-year-young upstart near
the core of the old and extensive Cepheus
OB1 Association star-forming region.
Returning to Delta Cephei, head
about 3¼ ̊ north-northeast to the 12th-
magnitude planetary nebula NGC 7354.
At 60x, the nebula appears as a 20" glow
with a bright core and a ghostly, somewhat
elongated outer halo. Moderate- to large-
aperture telescopes and magnifications
beyond 200x may reveal the collection of
bright knots that girdle the nebula.
Our next object, Caroline’s Spiral
Cluster (NGC 7789), lies 3 ̊ southwest of
2nd-magnitude Caph (Beta Cassiopeiae)
and was discovered by — who else? —
Caroline Herschel. Binoculars show it as
a circular “cloud of minute stars” that
sparkle in and out of view with averted
vision. Telescopically, this magnitude 6.5
cluster spans 25' of sky and is one of the
finest and richest open clusters. The chal-
lenge is to see it with your unaided eyes.
Returning to Caph, we slide about 30'
south-southeast to find the tiny (5')
ref lection nebula van den Bergh 1. This
pale breath of light is illuminated pri-
marily by three roughly 9th-magnitude
stars, burning through the haze like
streetlights seen through fog.
Now glide about 1¾ ̊ east and slightly
north of vdB 1 to the 10th-magnitude
dwarf irregular galaxy IC 10, a member
of the Local Group of galaxies, and the
closest known starburst galaxy. Knowing
that it lies 2.2 million light-years away
(closer than the Andromeda Galaxy) will
help you to appreciate its tiny size (7').Campbell’s Hydrogen Star is a planetary
nebula with a rare [WC] star at its core.
The object is named after its discoverer,
American astronomer William Campbell.
ANTHONY AYIOMAMITIS. INSET: ESA/NASA/HUBBLE