Cepheus, the King, has hidden
his treasure well, but not so well that curious amateurs can't find
more than enough to stuff their pockets. The pentagonal figure of Cepheus, the King, stands above Polaris at nightfall in October. Stellarium
When my kids were younger they loved to listen to the iconic In the Hall of the Mountain King from Edvard Grieg's Peer Gynt.
The music so perfectly captures Peer's desperate attempt to escape the
mountain trolls and the troll king. But just when all seems hopeless,
he's saved by the rays of the rising Sun and the sound of distant church
bells, two things the beasts cannot bear.
At nightfall in October, Cepheus, King of the Sky, looks down upon
the chilling earth and tempts skywatchers with similar riches. None of
us need fear his wrath — these treasures are free for the taking. I'm
always amazed how much Cepheus has to offer, so much that I'm only going
to describe a few of my favorites. While the constellation is
circumpolar from mid-northern latitudes and open for observation
year-round, it stands directly on the meridian at nightfall in early
October, making this the best time for observers at more southerly
latitudes to obtain their kingly rewards.
At the Foot of the King
Mu
Cep, the Garnet Star, shows off its color even in a pair of binoculars.
Its light is variable, ranging from magnitude 3.4 to 5.1 with a current
magnitude of 3.8. Aladin Sky Atlas
We'll start with one of the biggest and most distant stars easily visible with the naked eye, Mu (μ) Cephei, better known as the Garnet Star.
This red supergiant is 2,840 light-years away with a diameter more than
1,000 times that of the Sun. In my scope it's a tiny, yellow-orange
spotlight. Were Mu moved to Vega's distance of 25 light-years it would
shine at magnitude –8.3, more than 40 times brighter than Venus!
The
emission nebula complex IC 1396 is a rich, star-forming region about
3,000 light-years away and several hundred light-years wide. The
approximately 2.5°-wide object offers a candy store of deep-sky choices.
North is up in this and all photos unless noted. Digitized Sky Survey, ESA, ESO, NASA with composite by Davide De Martin
The wreath's northern half glowed brightest and was plain to see but no structure was evident, just a diffuse haze. Barnard 161,
located in the northern half of IC 1396, was an obvious dark spot,
especially with averted vision. Photos show a dark, 3′-wide cometary
"head" that widens and fades to the north. Dark nebula visibility is
rated by opacity from 1 for least opaque (most transparent) to 6 for
most opaque. B161's opacity is 6 and it contrasts well against the
surrounding nebulosity. I also saw hints of two other objects chewing
into the wreath's southern border — B160 (opacity = 4) and B165 (5).
Use
this map to help you find the our featured objects. Stars are shown to
magnitude 10 with double stars circled. North is to the right and south
to the left. Click for a large version you can download and use at the
telescope. Stellarium with additions by the author
But what really grabs your attention when you first arrive at IC 1396 is the remarkable triple/double star pair Σ2816 and Σ2819.
Σ2816 is a bright little bird winging across the nebula with a
5.7-magnitude primary flanked by two magnitude-7.5 stars at 12″ and 20″
to the northeast and northwest. Hands down one of the finest triples in
the sky for a small telescope. Look 12′ to the northeast and you can't
miss its cohort Σ2819, a pretty pair of stars (magnitudes 7.5 and 8.5)
separated by 13″. Both stars are members of the cluster Trumpler 37, the
loose assemblage embedded within the nebula.
The
reflection nebula Van den Bergh 142 is embedded within a larger dark
nebula nicknamed the Elephant Trunk Nebula. The bright triple star
Struve 2816 (left) will guide you to it. Aladin Sky Atlas
Finally, there is the Elephant's Trunk Nebula or Van den Bergh 142
(vdB 142), a dark, dusty cloud the edges of which are illuminated and
ionized by the triple star Σ2816 located about 18′ due east. A
reflection nebula is centered on the 12th-magnitude star in the "eye" of
the elephant.
To see it, remove the nebula filter and apply high
magnification (150× and up). It was subtle but I could make out a small,
round glow centered on the star like a distant candle seen through fog.
With the filter back in place, I used averted vision and
magnifications of 64× and 142× to spy the fingerlike dark "trunk" that
extends about 15′ to the west. I guess it looked like an elephant's
trunk but Cheetos came first to mind.
Doubling Up
From IC 1396 we head straight north into the heart of Cepheus to Xi (ξ) Cephei,
one of my favorite doubles. This 4.3-magnitude star splits into an
exquisite pair with magnitudes of 4.8 and 6.3 separated by 8″. They're
just close enough to each other and at 64× glimmer in a thrilling way
while maintaining the sharpness inherent in low-power views. You could
go higher but don't. Make your eye work just a teeny bit on this one. Before
moving on from Xi Cephei treat yourself to a wonderful little asterism I
ran into and dubbed the False Belt. Made of three 9th-magnitude stars
in a row just like Orion's Belt, this figure is only 1.2′ across. South
is up. Stellarium
Next, try 3rd-magnitude Beta (β) Cephei with a
7.8-magnitude companion 13.6″ to the southwest. The pair's relatively
close separation and similar magnitude difference make it look like a
slightly wider version of Xi Cep. The brighter star may not pique your
interest at first glance but that's only because of its enormous
distance of nearly 900 light-years. Beta blazes with a luminosity 23,000
times that of the Sun, and it's 13 times as massive. The cluster lookalike Alessi-Teutsch 5 is visible in all instruments and spans 7′. Aladin Sky Atlas
In the chart above I mentioned seeing a minute version of Orion's
Belt. Cepheus has another likely asterism worth a visit — a compact
knot of four 7th- and 8th-magnitude stars called Alessi-Teutsch 5
located about 2° northwest of Zeta (ζ) Cephei. A worthy pretender, it's
a neat sight in a pair of binoculars or your finderscope.
If you're looking for closer company, slide over to Omicron (ο) Cephei,
a tight, unequal duo with magnitudes of 5 and 7.3 separated by 3.4″. I
sliced them apart with 245× and enjoyed the primary's pleasing golden
tone. The secondary shines close by at position angle 224° (southwest). The carbon star S Cephei looks like a spicy red pepper in a small telescope right now. Aladin Sky Atlas
Before returning to the deep sky, we'll make one last stellar stop — S
Cephei, a deep-red carbon star that waxes and wanes from magnitude 7.4
to 12.9 and back every 487 days. Right now, it shines at 7.2 — close to
maximum — an easy sight in binoculars. Through my 15-inch a couple weeks
back it glowed a gorgeous cherry-red. For a detailed finder chart to
follow it from bright to faint, go to the AAVSO website, type S Cep in the Pick a Star box and then click Create a Finder Chart.
Back Into the Deeps
Do not leave Cepheus until you've looked at the Iris Nebula
(NGC 7023). This bright reflection nebula is illuminated by the
massive, pre-main-sequence star HD 200775, the 7th-magnitude object at
its center. At first glance you'll see the star swaddled in vague
nebulosity, but if you increase the magnification to 100× or more, an
amazing amount of structure emerges. The
Iris Nebula, named for the flower, is 1,300 light-years away and 6
light-years across. The massive, young star at center, HD 200775,
illuminates a region of space rich in dust grains. Light reflected from
the grains gives the nebula its blue color. Hunter Wilson
The brightest blob surrounds the central star while a fainter oval
patch is visible to its south, nearly touching. East of the central star
I saw a thick bar of luminous dust and a fainter, broader, less defined
glow to the west of the star. Photographs of the nebula recall an iris
bloom but visually it's closer to a tulip with the central star as the
pistil.
Another kingly sight is the pairing of the reflection nebula NGC 7129 with the rich open cluster NGC 7142.
NGC 7129 is a cluster in the making, and it fresh-faced stars are
responsible for illuminating their birth cloud, a 7′-wide nebula with an
overall magnitude of 11.5. I saw about a dozen stars swathed in
nebulosity with the brightest patches around the two brightest stars
(magnitudes 9.5 and 10.6). Another smaller condensation smears a fainter
star immediately to the northwest of the duo. Just ½° southeast in the
same field of view NGC 7129 may catch your eye. Don't
miss this wonderful pairing of reflection nebula NGC 7129 (top) and
open cluster NGC 7142. Both fit in the same low-to-medium magnification
field of view. Aladin Sky Atlas
Increase your magnification here to 100× or higher to better make out
the many faint stars packed into its 12′ diameter. The brightest is
11th magnitude, but most of the ~180 members glimmer at 13 or fainter;
together they create a fine mist of stars very pleasing to the eye. The
area is liberally sprinkled with interstellar dust which is in part
responsible for dimming the group. But that's not the only reason for
its faintness. NGC 7142 lies about 6,200 light-years away while its
apparent neighbor, NGC 7129, is only 3,300 light-years distant. Seeing
them together allows us to imagine them in three dimensions with the
nebula in the foreground and the cluster far, far away.
NGC
40 is a bright planetary nebula in northern Cepheus with a prominent
11.6-magnitude central star and diameter of 38″ × 35″. A pretty sight
with or without a nebula filter.
We've touched on asterisms, open clusters and nebulae but the Sky King is home to several fine planetary nebulae including NGC 40,
the brightest resident at magnitude 10.7. A sizzlingly hot white dwarf
with a temperature of 50,000°C occupies the center and blasts its former
atmosphere with energetic ultraviolet light, exciting it to glow. Using
magnifications of 142× and 245× on the 15-inch I made out a distinct
shell with a darker interior slightly elongated in the north-south
direction. The western half appeared brighter and more sharply defined
than the east. This planetary mimics the better known "Blinking
Planetary" NGC 6826 in Cygnus. If you stare hard at the bright central
star the nebula almost disappears. Switch back to averted vision and
boom — it reappears!
Although my pockets are bulging with deep-sky treasures after a visit
to the lair of King Cepheus I fear I've barely touched on the totality
of what the constellation offers. Take this as a first foray. I promise
we'll return another night.
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