Sky & Telescope - December 2018 - 54

DECEMBER 2018 OBSERVING
Deep-Sky Wonders by Sue French
FIND YOUR CLUB:
skyandtelescope.
com/astronomyclubs-organizations.

The Frosty Sky
The stars are glittering in the frosty sky,
Frequent as pebbles on a broad sea-coast;
And o'er the vault the cloud-like galaxy
Has marshalled its innumerable host.
- Charles Heavysege, Sonnet XIV, 1865

∑131

M103

p M103 is a modest smudge of light northeast
of Delta Cassiopeiae. Look for the 7.3-magnitude primary of double star STF 131 in the
northwest region of the cluster.

DECE MBE R 2 018 * SK Y & TELESCOPE

ecember nights fall crisp and cold
at mid-northern latitudes, when
even the Milky Way seems like a wreath
of frost condensed along some join in
the vault of the sky. One of the constellations softly silvered by its light
is Cassiopeia, the Queen; high in the
northern sky we now see her brightest
gems forming an M for Her Majesty.
Alpha (Į) Cassiopeiae is ofﬁcially
the constellation's brightest star at magnitude 2.24, although nearby Gamma
(γ) Cas is an eruptive, irregular variable star that sometimes outshines it.
Alpha is an orange giant star, 42 times
the Sun's diameter, sitting about 228
light-years away from us. This star is
commonly known as Shedar, derived
from an Arabic word meaning "the
breast" and denoting its position in the
traditional constellation ﬁgure, which
portrays our celestial Queen sitting
with her head to the west.
In 1780 William Herschel discovered
a fainter star 53″ northwest of Alpha.
He described the pair as extremely
unequal with colors of pale red for the
bright star and "dusky" for its companion. These stars are even more widely
separated now, and through my 130mm refractor at 37×, I see the primary
as deep yellow and the 8.8-magnitude
attendant, roosting west-northwest, as
yellow-orange. A study of the relative
motion of the components proves this is
merely an optical double rather than a
genuine binary.
Between Delta (δ) and Epsilon (ε)
Cassiopeiae rests a queenly quartet
of open clusters whose most visited
member is Messier 103, discovered
by Charles Messier's colleague Pierre
Méchain with a 3-inch refractor in

1781. Despite its modest appearance,
M103 is a true cluster, but the number
of probable members differs wildly from
source to source depending on the criteria applied. Modern values range from
77 to 526 stars.
M103 offers fewer stars to the
backyard telescope but is a pretty group
nonetheless. The 130-mm scope at
37× reveals a 5′ triangle of 13 bright to
faint stars. The three most prominent
sparks lie along the northeastern side
of the triangle, with the brightest one
at the triangle's pointy end. This is the
double star Struve 131 (STF 131 or
Σ131), whose companion is easily visible
13.9″ to the southeast. At 117× I tally 23
stars dotting the triangle, plus several
stars sprinkled outside the triangle's
long sides. The middle star of the trio
that deﬁnes the triangle's northeastern
side smolders deep orange. My 15-inch
reﬂector at 216× teases out 40 to 45
stars within roughly 6′.
If I place M103 in the west-southwestern edge of the refractor's 37× ﬁeld
of view, the wide-angle eyepiece lets me
cram NGC 663 into the scene as well.
It's a beautiful group of 25 fairly bright
to very faint stars, its core dusted with
the powdery light of unresolved suns.
Centering NGC 663 draws the last two
members of the open cluster quartet
into view, NGC 654 and NGC 659,
both much smaller than their neighbor.
The former is a bright mist stippled
with a splash of diamond-dust stars. A
few slightly more conspicuous jewels
decorate the fringes, and a golden, 7thmagnitude star burnishes its southeastern edge. NGC 659 is simply a knot of
ﬁve faint stars with perhaps a feathering of ﬁne fog.

DOUG GERMAN

Bundle up and go out into the cold. Your queen awaits.

Sky & Telescope - December 2018

Table of Contents for the Digital Edition of Sky & Telescope - December 2018