Sky & Telescope - December 2020 - 54

DECEMBER 2020 OBSERVING
Deep-Sky Wonders by Sue French

To celebrate 20 years of Sue French's
stellar contributions to Sky & Telescope, we have been sharing the best
of her columns throughout 2020.
We have updated values to current
measurements when appropriate.

The Starry Heavens
Clusters and nebulae abound in compact Cassiopeia.
Ye quenchless stars! so eloquently bright,
Untroubled sentries of the shadowy night,
While half the world is lapp'd in /
downy dreams,
And round the lattice creep your /
midnight beams,
How sweet to gaze upon your placid eyes,
In lambent beauty looking from the skies!
- Robert Montgomery,
The Omnipresence of the Deity, 1828

S

everal bright and shining eyes gaze
down at us from Cassiopeia, and a
wealth of lesser lights join them from
their favored position along the crowded
plane of our galaxy, where reigns the
Milky Way in soft and misty splendor.
Many of the constellation's twinkling peepers are gathered into star
clusters, with NGC 7789 being one of
2h 00m

ε

637

and reveals far too many stars to count,
with the brightest weighing in at 10th
magnitude. The fainter the stars, the
more numerous they become, until
they coalesce into a stippled haze in the
cluster's teeming, 12′ core.
NGC 7789 is a spectacular sight
when viewed through my 10-inch
reflector at 70×. Its panoply of stars
is enchantingly filigreed with inky
black threads that wind through the
cluster. Off the group's northeastern
side, the double star Espin 38 displays
a yellow-white primary with a ruddy
companion to its west-southwest. The
companion is a carbon star that varies
from magnitude 9.9 to 12.7. Sometimes called Wildt's Red Star, after
the German-American astrophysicist
Rupert Wildt, this variable is currently

the most beautiful stellar gatherings in
our sky. The cluster shares a low-power
field of view with the yellow hypergiant
Rho (ρ) Cassiopeiae. A yellow hypergiant is a highly luminous supergiant that
suffers prodigious mass loss, as well as
occasional eruptions that dim the star
with a cloak of ejected material. If Rho
replaced our Sun, it would extend out
beyond Mars to the inner edge of the
asteroid belt.
NGC 7789 is easily visible through
my 8×50 finderscope as a sizable,
grainy glow. My 130-mm refractor at
23× unveils a beautiful cluster richly
populated with pinpoint stars. An
orange, 8th-magnitude star on the
group's western fringe helps me assign
an apparent diameter of 20′ to the
cluster. NGC 7789 is stunning at 63×

1h 30m

1h 00m

0h 30m

23h 30m

0h 00m

IC 1747
559

κ
654

Sh 2-173

CASSIOPEIA

663

381

743

M103

659

Star magnitudes

χ
3
4
5
6
7
8
9

12

225

103

129

υ2

436

457

φ

IC 10

τ
ρ

Espin 38

η

Queen's
Kite

7789

744

σ
α

θ

DECEMBER 2 02 0 * SK Y & TELESCOPE

β

υ1

281

54

+60°

γ

δ
Sh 2-188

7790

136

μ

+55°



Sky & Telescope - December 2020

Table of Contents for the Digital Edition of Sky & Telescope - December 2020

Contents
Sky & Telescope - December 2020 - Cover1
Sky & Telescope - December 2020 - Cover2
Sky & Telescope - December 2020 - 1
Sky & Telescope - December 2020 - Contents
Sky & Telescope - December 2020 - 3
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