Sky & Telescope - February 2021 - 24

Colorful Planetaries

ies, long exposures with a Hα ﬁlter resolve
ments show complex dark lanes throughits faint outer shells that nearly double
out this ancient planetary.
the apparent extent of this object. Larger
All of the nebulae discussed above
instruments will also capture the nearby
appear more or less circular, but there are
14th-magnitude spiral galaxy IC 1296,
exceptions, such as the aptly named Squid
located less than 4′ northwest of M57.
Nebula (Ou4). Its length is 2.5 times the
Moving about 17° east into Cygnus
Moon's diameter, equivalent to a true
brings
us to PN G75.5+1.7, better known
dimension of more than 50 light-years.
S EAGLE'S BALL NGC 6781 in Aquila
Ou4 appears to lie within, and at the
as
the
Soap
Bubble Nebula. This spherical
displays a subtle dark star-shape in its
same distance as, Sh2-129 (the Flying
shell resembles Abell 39, but because it
inner regions.
Bat Nebula), a huge hydrogen-rich region
resides in a ﬁeld awash in H II nebulosin Cepheus. If you want to capture the Squid, plan to rack
ity, it went unnoticed until 2008. You'll need to accumulate
up the exposure time: I needed more than 60 hours of O IIIlots of exposure time to capture this one. It's most evident
ﬁltered light before I was satisﬁed with the resulting image.
in frames shot through a Hα ﬁlter. Fortunately, it's easy to
ﬁnd roughly 2/3° east-southeast of the Crescent Nebula, NGC
6888. Both ﬁt comfortably in the same 1.5° ﬁeld southwest of
Summer Gems
Sadr, Gamma (γ) Cygni.
A rich and famous imaging target, M27, the Dumbbell
Heading south to Aquila we ﬁnd NGC 6781, a moderately
Nebula, resides in Vulpecula. At about 8′ × 4′ in size, it's both
large and bright for a planetary. Even relatively short expolarge, circular PN 1.8′ in diameter. This nebula has one sharp
sures show the apple-core-shaped interior of the nebula, and
and one soft edge. Even though it has a true diameter of more
long exposures give it the shape of a richly textured, teal-and- than one light-year, it appears small because of its great disred football. Patient imagers who go deep with narrowband
tance, of around 2,500 light-years.
ﬁlters can pick up its faint, extended shells of glowing Hα and
I ﬁnd Abell 39 in Hercules to be one of the most enigO III, nearly doubling M27's apparent size.
matic planetaries in the sky. This tenuous, teal-colored sphere
Perhaps the best known planetary of all is M57, the Ring
resembles a ghostly green crystal ball. With a diameter of
around 2.5 light-years, it's the largest known near-perfect
Nebula, in Lyra. It appears in the eyepiece as a 76″-long oval
spherical object. Deep images with large scopes show a few
of greyish smoke in most any sized instrument, but even
distant galaxies behind the nebula's translucent veil.
short exposures show its rich red, yellow, and teal hues. This
Farther to the north, NGC 6543, the Cat's Eye Nebula, is
well-known PN sports a mottled texture in its outer edge and
a couple of stars in the central region. As with other planetar- a small, bright object of about 20″ diameter, making it the

Planetary Nebulae
Object
M97
M76
NGC 246
NGC 2392
Abell 31

Constellation
Ursa Major

Mag(v)
9.9

Size

Dec.

2.8′

11h

15m

+55° 01′

42m

-51° 34′

Perseus

10.1

67″

01h

Cetus

10.9

4.1′

00h 47m

-11° 52′

19.5″

07h

29m

+20° 55′

08h

54m

+08° 55′
+59° 59′

Gemini

9.2

Cancer

17′

Ou4

Cepheus

150′ × 30′

21h 12m

M27

Vulpecula

7.3

8′ × 4′

20h 00m

+22° 43′

M57

Lyra

8.8

76″

18h 54m

+33° 02′

Cygnus

4.3′

20h 15m

+38° 03′

18m

+06° 33′

PN G75.5+1.7
NGC 6781
Abell 39
NGC 6543

Aquila

11.4

1.8′

19h

Hercules

2.6′

16h 28m

+27° 55′

8.1

20″

17h

59m

+66° 38′

22h

30m

+20° 48′

23h 26m

+42° 33′

Draco

NGC 7293

Aquarius

7.3

16′ × 12′

NGC 7662

Andromeda

8.3

17′

Angular sizes are from recent catalogs. Photographically, an object's size is often larger than the cataloged value. Right ascension and declination are for equinox
2000.0.

FEBRUARY 2 021 * SK Y & TELESCOPE

Sky & Telescope - February 2021

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