Sky & Telescope - December 2020 - 55

POSS-II / CA LTECH / PA LO M A R OBSERVATORY

near peak brightness. When I boost the
telescope's magnification to 115×, NGC
7789's core stars seem to be arrayed in
a strange, spiral pattern that unwinds
clockwise from the center for more
than 1½ turns.
Beta (β) Cassiopeiae, also known
as Caph, lies halfway between NGC
7789 and the large emission nebula
Sharpless 2-173, and 5th-magnitude
12 Cassiopeiae guards the nebula's eastnortheastern edge. The inconspicuous
star cluster Mayer 1 rests at the heart of
the nebula, with a 7th-magnitude star
marking its south-southwestern edge.
Through my 105-mm refractor at
47×, all I can see of Mayer 1 is a bent
band of 10 stars. The brightest one is
magnitude 9.5 and defines the cluster's
center. These stars are entangled in a
feeble glow that spreads southward to
a 4′ trapezoid of 9th- and 10th-magnitude stars. The most prominent part of
the nebula is a misty arc northwest of
Mayer 1. A dark void between it and the
cluster nicely delineates the arc's concave inner edge, and a pretty, reddishorange, 7th-magnitude star adorns the
outer edge. Very faint nebulosity weds
this arc to the amorphous glow south of
the cluster.
Although filters don't help much
with the little refractor, a narrowband
nebula filter works fairly well with my
10-inch reflector at 68×, expanding
Sh 2-173 and emphasizing the dark gap
between the arc and Mayer 1. Except
for this fairly bright arc, the nebula's
outer regions are vague. I'd guesstimate
a maximum width of 18′ to 20′.
Mayer 1 was introduced in a 1964
paper by Pavel Mayer entitled "List of
Open Star Clusters in Emission Nebulae." It appeared in the Czech journal
Publications of the Astronomical Institute
of the Charles University (Acta Universitatis Carolinae. Mathematica et Physica).
The three clusters designated "Anon."
(anonymous) in Mayer's list now bear
his name.
Dropping ½° southward from 12
Cassiopeiae with my 130-mm refractor at 37×, I see a small, elongated,
granular, fuzzy patch with two stars at
its northeastern end. This is the open

Espin 38

S NGC 7789 is extraordinarily rich and old as open clusters go. The wide range of colors among its
stars is due to the fact that many have evolved into red giants. Espin 38 is seen at the upper left.

cluster NGC 103. At 102× ten stars
emerge from the haze, and a half dozen
stars scattered around them fill the
group out to a diameter of 3½′. Through
my 10-inch reflector at 187×, I count 30
stars within a diameter of 5′. Many are
gathered into a bar that tapers southwest, and most of the rest form two
drooping arms that sprout from each
side of the bar's wide end.

NGC 136 sits just 46′ east-northeast
of NGC 103. At 102× the 130-mm
refractor readily shows a subtly flecked,
diminutive patch of haze, though it does
appear rather faint. The cluster spans
1¼′, and a very dim star dots its northnortheastern edge. NGC 136 is lovely
through my 10-inch scope at 115×. It
brings to mind a little mound of beach
sand sparkling with minuscule grains.

Clusters, Stars, and Nebulae in Cassiopeia
Object

Type

Mag(v)

Size/Sep

RA

Dec.

NGC 7789

Open cluster

6.7

25′

23h 57.5m

+56° 43′

Espin 38

Double star

9.8, 10.7

24″

23h 59.1m

+56° 58′

21.9m

+61° 44′
+61° 19′

Sharpless 2-173
NGC 103
NGC 136
Queen's Kite
NGC 743
IC 1747

Emission nebula

-

25′

00h

Open cluster

9.8

5.0′

00h 25.3m
00h

31.5m

+61° 31′

Open cluster

11.5

1.5′

Asterism

-

4.0° × 2.3°

01h 37.8m

+57° 23′

Open cluster

9.5

8.0′

01h 58.6m

+60° 09′

13″

01h

+63° 19′

Planetary nebula

12.0

57.6m

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.

sk yandtelescope.org * DECEMBER 2 02 0

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