Sky and Telescope - July 2017 - 55

Ring Nebula

SK E TCH: SUE FRENCH; DU MBBELL NEBUL A: WEST VIE W OBSERVATORY / CC BY-SA 4.0;
G RE AT HERCULES CLUSTER: SERGIO K A MINSK Y

p The author's sketch of M57, the Ring Nebula,
as seen through her 130-mm refractor at 234×,
shows the nebula's gauzy, circular interior.

Those who hunt more difﬁcult
game can stalk M57's 15th-magnitude
central star. Although folks have snared
it through scopes as small as 8 inches
in aperture, I've never nabbed it with
anything smaller than my 14.5-inch.
The key to a successful sighting lies
in having exceptionally good seeing
(atmospheric steadiness) and very high
magniﬁcation.
Although M57 looks like a simple
ring, its structure is actually much more
complicated. You could think of it as a
bright doughnut wrapped around the
middle of a faint football, all embedded
in a complex, tenuous halo. The ring
structure dominates largely because
we're gazing down the pole of the
planetary nebula. If we could see the
Ring Nebula from the plane of its equator, it might look much like our next
object, the Dumbbell Nebula (M27) in
Vulpecula, the Little Fox.

Swept up by Charles Messier in 1764,
M27 was the ﬁrst planetary nebula ever
discovered. It rests 24′ south-southeast
of 14 Vulpeculae and can be recognized
in my 9×50 ﬁnder. When seen through
my 130-mm scope at 23×, the Dumbbell Nebula looks substantially larger
than the Ring Nebula. Its bright region
is shaped like an apple with the sides
munched away. Protruding from the
sides of this apple core is a dimmer
region that turns the nebula into a football. At 48× the apple core's rims shine
brightest, and its pinched-in sides are
more obvious. There's also a fairly bright
bar diagonally connecting the caps from
east-northeast to west-southwest. The
football extensions stand out best at
63×, but it's a rather plump football.
Upping the power to 164× the apple core
displays brighter wedges hugging the
narrower angles where the bar meets
each cap. At 234×, the southwestern
wedge seems brighter than its counterpart in the northeast.
The Dumbbell's central star is easier
to spot than the Ring's, but it's still no
walk in the park. The smallest scope I've
seen it in was my husband's erstwhile
140-mm refactor, employing a magniﬁcation of 300×.
Let's move on to the Great Hercules
Cluster (M13), a group of more than
200,000 stars about 23,000 light-years
away from us. Most globular clusters
are not conﬁned to the disk of our
galaxy but instead follow inclined orbits
and spend much of their time in the

Dumbbell Nebula

p The Dumbbell Nebula looks like a wellgnawed apple core in the eyepiece. Upping
the magnification may reveal extensions more
evocative of an American football.

Great Hercules Cluster

Propeller

p M13, the Great Hercules Cluster, resolves
from mist to a spangle of brilliant pinpoints
with enough magnification. This globular takes
magnification well. Increase the aperture to 10
inches or more and raise the magnification to
100× to 200×, and you should be able to see
the trio of dark lanes known as "the Propeller."
Look southeast of the cluster's core.

Sue's Summer Favorites
Object
Ring Nebula (M57)

Type

Mag(v)

Size/Sep

Dec.

Planetary nebula

8.8

1.6′ × 1.1′

18h 53.6m

+33° 02′

19h

59.6m

+22° 43′

16h 41.7m

+36° 28′

04.1m

-24° 18′

Dumbbell Nebula (M27)

Planetary nebula

7.4

8.0′ × 5.5′

Great Hercules Cluster (M13)

Globular cluster

5.8

20′

Lagoon Nebula (M8)

Emission nebula

3.0

45′ × 30′

18h

Omega Nebula (M17)

Emission nebula

5.5

20′ × 15′

18h 20.8m

-16° 10′

17h

-32° 16′

Butterﬂy Cluster (M6)

Open cluster

4.2

33′

40.3m

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.

s k y a n d t e l e s c o p e .c o m

* J U LY 2 017

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Sky and Telescope - July 2017

Table of Contents for the Digital Edition of Sky and Telescope - July 2017