Sky & Telescope - July 2021 - 40

Favorite Open Clusters

NGC 6352. The open cluster is 1° west of Alpha. It's very
attractive, featuring loops and chains of 70 equal-magnitude
jewels enclosing voids. The lucida is orange, as is often the case
with galactic clusters. While my views were from Australia,
I've included IC 4651 on this list because it can be observed
from the southern half of the U.S.; and open clusters suffer
less from low altitude than any other class of deep-sky object.
Finishing in Vulpecula we come to NGC 6940, which
William Herschel discovered in 1784. It's 3.4° southwest of
52 Cygni, the star that pins the western section of the Veil

Contributing Editor ALAN WHITMAN developed a greater
fondness for viewing inside his observatory when bent over
an eyepiece, neck exposed, after a cougar neatly butchered a
deer on his front lawn.
INVALUABLE RESOURCE
Alan thanks Steve Gottlieb for creating and maintaining his excellent website on the history of NGC and IC objects and invites you
to visit it at https://is.gd/AstronomyMall.

Favorite Summer Open Clusters
Object

Constellation

Mag(v)

Size

M11

Scutum

5.8

11′

Scorpius

4.2

33′

17h 40.3m

-32° 16′

Scorpius

3.3

75′

17h 53.8m

-34° 47′

NGC 6231

Scorpius

2.6

14′

16h 54.2m

-41° 50′

Sagittarius

5.5

25′

17h 56.9m

-19° 01′

70′

17h

46.2m

+05° 43′

27.2m

+06° 30′

M23
IC 4665
NGC 6633
IC 4756
NGC 7789

Ophiuchus

4.2

51.1m

Dec.

18h

-06° 16′

Ophiuchus

4.6

20′

18h

Serpens Cauda

4.6

40′

18h 38.9m

+05° 26′

25′

23h

57.5m

+56° 43′

24.7m

-49° 55′
+28° 17′

Cassiopeia

6.7

Ara

6.9

10′

17h

NGC 6940

Vulpecula

6.3

25′

20h 34.5m

NGC 6819

Cygnus

7.3

5′

19h 41.3m

+40° 11′

NGC 6939

Cepheus

7.8

10′

20h 31.5m

+60° 40′

Cassiopeia

6.9

16′

23h 24.8m

+61° 36′

IC 4651

M52

Angular sizes 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.

J U LY 2 0 2 1 * S K Y & T E L E S C O P E

Honorable
Mention . . .
. . . goes to three rich clusters in the northern Milky
Way: NGC 6819, some
7.8° west of Gamma (γ)
Cygni, one of Caroline Herschel's discoveries with her
comet-seeker; NGC 6939
in Cepheus, lying 2°
southwest of Eta (η) Cephei
and sharing a field of view
with the fine, multi-armed,
face-on spiral galaxy NGC
6946; and western Cassiopeia's Messier 52 (in
the same field of view as
the famous but faint Bubble
Nebula). Extend the line
from Alpha to Beta Cassiopeiae by slightly more than
one length and you will land
directly on M52.

NGC 7789: VOLK ER WENDEL / STEFA N BINNE WIES / JOSEF PÖPSEL /
CA PELL A OBSERVATORY; SK E TCH: GU Y M ACKIE

S CAROLINE'S ROSE Can you see the arcs and swirls of stars and dark
lanes that give NGC 7789 its nickname?

Nebula. My ﬁrst view of NGC 6940 was when
I chanced upon it while sweeping the Milky
Way with 7×50 binoculars. It was unresolved in the binoculars, but after observing it with my 8-inch at 50× on a superb
night I wrote: " What a beauty - deﬁnitely
a splendor! A large rich cluster of 60 stars
in a very rich Milky Way ﬁeld, its stars
are arranged in a bulbous Y-shape. That is,
each arm of the Y is composed of clouds of
stars, rather than a single line. A reddish star
marks the center. " Through my 16-inch at 141×
it's fairly well separated from the Milky Way ﬁeld
and comprises - by my estimation - about 200 stars
of fairly equal magnitude. There's an oval of stars preceding
and a tail of stars following.
I hope you enjoyed this ramble through the skies visiting
my favorite open clusters. Maybe one day some of these will
become your favorite targets, too.

https://www.is.gd/AstronomyMall

Sky & Telescope - July 2021

Table of Contents for the Digital Edition of Sky & Telescope - July 2021