Sky and Telescope - July 2016 - 58

OBSERVING

Deep-Sky Wonders

whereas those belonging to NGC 6287 lose nearly two
magnitudes.
Moving beyond the clusters mentioned by Serviss,
you'll ﬁnd NGC 6235 1.2°° northwest of 24 Ophiuchi. It's
easily visible in my 105-mm scope at 47×, with an 11thmagnitude star close to its north-northwestern edge. At
87× the cluster is a 3′ globe that grows brighter toward
the center. A few extremely faint stars freckle the cluster
in the 10-inch scope at 115×, and a dash more emerge at
231×. NGC 6235 is 38,000 light-years distant. Its brightest star is magnitude 14.0, and it suﬀers one magnitude
of extinction.
Our next globular cluster is NGC 6325. Look for
it 31′ due north of Omicron (ο) Ophiuchi, a pretty
Left: NGC 6369, shown
here in a composite image
taken by the Wide-Field
Planetary Camera 2 on the
Hubble Space Telescope,
lies about 2,000 to 5,000
light-years from Earth.
Below:
e o Bertrand Laville
sketched
the ghostly
s
ﬁgure of NGC 6369
as seen through a
450-mm Dobsonian at 257× while
he was observing
in San Pedro de
Atacama,
Chile.
At

NGC 6369

Objects in Ophiuchus
Object
M19
NGC 6293

Type

Mag(v)

Size/Sep

Dec

Globular cluster

6.8

17′

17h 02.6m

-26°° 16′

8.2′

17h

10.2m

-26°° 35′

04.5m

-24°° 46′

Globular cluster

8.2

NGC 6284

Globular cluster

8.8

6.2′

17h

NGC 6287

Globular cluster

9.4

4.8′

17h 05.2m

-22°° 43′

NGC 6235

Globular cluster

10.0

5.0′

16h 53.4m

-22°° 11′

10.3

4.1′

17h

18.0m

-23°° 46′

17h

18.0m

-24°° 17′

NGC 6325

Globular cluster

ο Oph

Double star

5.2, 6.6

10.0″″

B72

Dark nebula

34′ × 16′

17h 23.8m

-23°° 42′

Planetary nebula

11.4

38″″

17h 29.3m

-23°° 46′

4.8′

17h

-23°° 55′

NGC 6369
NGC 6401

Globular cluster

9.5

38.6m

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.

July 2016 sky & telescope

double with a 5.2-magnitude gold star accompanied
by a 6.6-magnitude yellow companion 10″ to its north.
The cluster is just a tiny fuzzspot through the 105-mm
refractor at 17×, while at 87× it's a 1½′ ball with a slightly
brighter center. In the 10-inch reﬂector at 115× the
cluster becomes a granular 2′ haze. It's little wonder that
I couldn't detect stars in this cluster, because its brightest member weakly shines at magnitude 15.2. In this
month's tour, NGC 6325 is the closest cluster to us at
25,000 light-years, but its stars undergo 2.8 magnitudes
of extinction. The dark nebulae riddling this patch of sky
are to blame for this severe brightness loss. It's like looking at the cluster through a sooty window.
Barnard 72 is a unique scrap of inky dust sitting
1.3° east of NGC 6325. The dark nebula's sinuous form
earns B72 its common name, the Snake Nebula, as well
as a place among favorites for imagers (see page 41). My
home sky isn't dark enough for a pleasing view of the
nebula, but from the northern reaches of New York's
Adirondack mountains with my dad's old 6-inch reﬂector, I can see the most prominent part as a 17′-tall S
charcoaled on the backdrop of the Milky Way.
Continuing our eastward trek, we'll encounter the
planetary nebula NGC 6369, also known as the Little
Ghost, perched 31′ west-northwest of 51 Ophiuchi.
It's quite petite in my 105-mm scope at 47× but stands
out well with a narrowband nebula ﬁlter at 122×. At
166× with an O III ﬁlter, the 10-inch scope transforms
the nebula into a splendid little ring. The annulus is
brighter along its northern rim, which contains a nearly
stellar bright spot. Folks with larger scopes might like to
try for the nebula's 15.1-magnitude central star.
We'll conclude our deep-sky tour with one last globular cluster, NGC 6401, found 1.6° east of 51 Ophiuchi
in an area rife with dark nebulae. Through the 105-mm
scope at 47×, the cluster is too small to reveal features,
but at 87× I can see that it has a brighter core. At 127×
the NGC 6401 spans 1½′, and a 12th-magnitude foreground star is conspicuously superimposed on the eastsoutheastern fringe of the core. Even my 10-inch scope
at 213× won't pry any stars from the haze, but merely
proﬀers a slight mottling of the 1¾′ glow.
NGC 6401 dwells 35,000 light-years away from us,
and its brightest star meets our eyes at a feeble apparent
magnitude of 15.2. With so many dusty nebulae threading this region, it's not surprising that NGC 6401's stars
are muted by 2.3 magnitudes of extinction.
As Serviss wrote, these starry swarms are sometimes
"more interesting for what they signify than for what
they show." We know them for the great star cities they
truly are, and they teach us about our view through the
dusty galaxy that we call home. ✦

Sky and Telescope - July 2016

Table of Contents for the Digital Edition of Sky and Telescope - July 2016