Sky & Telescope - July 2019 - 56

JULY 2019 OBSERVING
Deep-Sky Wonders

p Higher magnifications reveal NGC 6210 to
be elongated east-west. This high-resolution
image taken by the Hubble Space Telescope
reveals the true complexity of the planetary
nebula's structure. The central star is surrounded by a burgeoning gas bubble, behind
which filaments and pillars of excited hydrogen
gas appear.

26′ due east to a 9.8-magnitude star at
the northern corner of a 15′ trapezoid
formed with three slightly brighter
stars. A line drawn from the trapezoid's
western star through its northern one
and continued for the same distance
again will take you right to Abell 39.
When I ﬁrst visited Abell 39 with
my 10-inch reﬂector, I could spot it
only using averted vision and an O III
ﬁlter. Since familiarizing myself with it,
I've been able to view the nebula while

p The planetary nebula Abell 39 is a ghostly
haze in even large-aperture scopes like the
32-inch Ritchey-Chrétien used to capture this
image. Averted vision and an O III filter may
help improve the view for smaller scopes.

gazing directly at it. Abell 39 is round,
vaguely annular, and moderately large
for a planetary - almost 3′ across. A
magniﬁcation of about 70× gives me the
best view. Other observers have managed to nab this elusive planetary with
8-inch scopes. Can you?
¢ Contributing Editor SUE FRENCH
shared this Deep-Sky Wonders column
in the July 2007 issue of Sky & Telescope.

Harbored in the Hero
Object
Rasalgethi

Type
Double star

Mag(v)
3.5, 5.4

Dec.

MSA

4.7″

17h

14.6m

+14° 23′

1251

87L

17h

11.4m

Size/Sep

DoDz 7

Asterism

10′

+15° 29′

1251

87L

Sudor Ophiuchi

Asterism

~3½°

17h 01.1m

+14° 13′

1251

87L

Double star

5.9, 6.2

305″

17h 03.7m

+13° 36′

1251

87L

Asterism

100′ × 15′

16h

18.1m

+13° 03′

1254

87R

Double star

8.5, 9.6

7.4″

16h 12.1m

+11° 55′

1254

87R

Planetary nebula

10.7

13″ × 10″

11.7m

+12° 04′

1254

87R

Double star

5.1, 6.2

27″

16h 08.1m

+17° 03′

1230

87R

32.4m

+19° 50′

1229

69L

44.5m

+23° 48′

1204

69L

16h 27.6m

+27° 55′

1181

69L

∑4033

Harrington 7
∑ 2016

IC 4593
κ Herculis
NGC 6181

Spiral galaxy

16h

11.9

2.5′ × 1.1′

16h
16h

NGC 6210

Planetary nebula

8.8

20″ × 13″

Abell 39

Planetary nebula

13.0

170″

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. The columns headed MSA and U2 give the appropriate chart
numbers in the Millennium Star Atlas and Uranometria 2000.0 Deep Sky Atlas, respectively. All the objects this month are in the area of sky covered by Charts 54
and 55 of Sky & Telescope's Pocket Sky Atlas.

J U LY 2 0 1 9 * S K Y & T E L E S C O P E

NGC 6210: ESA / N ASA / HUBBLE SPACE TELESCOPE; A BELL 39: A DA M BLOCK / M OUN T LEM M ON
SK YCEN TER / UNIV ERSIT Y OF A RIZON A / CC BY-SA 3.0

ing the magniﬁcation to 87×, I see a
small north-south oval with a broadly
brighter core.
A pair of 7th-magnitude stars spaced
17′ apart lies two-thirds of the way
from Beta to 51 Herculis. The bright
planetary nebula NGC 6210 sits 9′
west-northwest of the duo's northeastern star. I can spot the nebula even at
17× through my 4.1-inch refractor. At
87× this pretty, blue-gray nebula almost
overpowers its 12th-magnitude central
star. A faint halo rims the planetary.
NGC 6210 looks greenish blue through
my 10-inch reﬂector, and at high power
it's elongated east-west. Deep images of
NGC 6210 show unusual projections
that earn this planetary its nickname,
the Turtle Nebula.
Our ﬁnal target is another planetary nebula, a very challenging one:
Abell 39 (PK 47+42.1). The nearest star
with a Bayer designation is Upsilon (υ)
Coronae Borealis. From Upsilon, hop
1.7° east-southeast to a golden 7.5-magnitude star, the brightest in the area,
and then drop 39′ south-southeast to
an 8.6-magnitude star. Next sweep

Sky & Telescope - July 2019

Table of Contents for the Digital Edition of Sky & Telescope - July 2019