Sky & Telescope - September 2016 - 55

Sue French

Star magnitudes

Sue French welcomes your comments at scfrench@nycap.rr.com.

+26°

10

3
4
5
6
7

20h 00m

η

19h 50m

19h 40m

19h 30m

Sh 2-88

α
VULPECULA

13
14

8
+34°

17

+24°

Σ 2576

χ

6820

Star magnitudes

12
M27
+22°

+32°

CYGNUS

6827
Roslund 3

η

9
M71

ζ
9

δ
α

Sh 2-84
20h 00m

19h 50m

φ

+30°

β

19h 40m

9

SAGITTA
+18°
19h 30m

southwest of Sh 2-84 is often mentioned in the same
breath as the nebula, it isn't widely accepted as the
nebula's illuminating star.
Also in Sagitta, the open cluster Roslund 3 ﬁnds its
home 1.0°° due north of Gamma (γ). Look for it along a
prominent, ¾° smile of stars, concave north-northeast. My
130-mm refractor at 37× plucks out a circlet of several stars
within the cluster, 10th magnitude and fainter. At 117× the
group morphs into a 5′ × 3′, east-west ovoid composed of
a dozen moderately bright stars and about as many faint
ones. The 15-inch scope at 216× discloses 29 stars, the
brightest forming a circle in the ovoid's eastern half.
Roslund 3 is one of seven new clusters found in 1960
by Curt Roslund during a survey of high-luminosity
stars in the northern Milky Way.
Crossing over the border into Vulpecula, we can pay
a visit to NGC 6827, 1.5° south-southwest of 12 Vulpeculae. This cluster hosts throngs of stars, mostly too faint
to see through small telescopes. We owe this to the cluster's distance of 13,000 light-years and a heavy dose of
interstellar dust along our line of sight. The dust absorbs
and scatters light, thus dimming the stars by more than
three magnitudes. Hundreds of stars are considered possible members of this cluster.
With my 130-mm refractor at 102×, I see NGC 6827
as a weak, ashen glow accompanied by 11th-magnitude
stars 2′ south-southeast and 3′ north. At 164× the cluster
appears slightly granular and spans about 2½′. A few
extremely faint stars peek out from the haze. Even
through a friend's 12.5-inch scope at 249×, I counted
only eight stars in the cluster. Can you do better?

β

+28°

One evening with my 15-inch scope and no particular
plan, I looked in on Sharpless 2-88, an emission nebula
40′ southeast of 10 Vulpeculae. At 79× an amorphous
nebula appeared, sprawling about 14½′ north-south and
8′ east-west. Two 10th-magnitude stars line the nebula's
western side, the northern one supplying the energy that
makes Sh 2-88 shine. Several stars are superimposed on
the nebula, including a 2′ trapezoid of stars (magnitudes
11.5 to 12.6) embedded in the eastern side.
While observing Sh 2-88, I noticed a small, detached
glow containing an 11.8-magnitude star slightly oﬀset
from its center. To locate it, look for a widely spaced pair
of bright stars (magnitudes 6.7 and 8.8) about 12′ southsoutheast of Sh 2-88. The little wisp ﬂoats 3.5′ north
of the brighter star and is named Sh 2-88A. Boosting
the power to 102×, Sh 2-88 stood out much better, and I
spotted a fainter fragment of ﬂuﬀ just 2.6′ east-northeast
of the ﬁrst. Designated Sh 2-88B, it's tipped northnorthwest and wears three faint stars: one at its southern
tip and two in its northern end. These petite nebulae
each span about 1′ and shine by both reﬂection (scattering) and emission of light.

Pi Aql

S

γ

7
+20°

4
5
6
7
8

DA

RIN

EV

AN

With a separation of only
1.5″, Pi Aquilae is a tight
double, but it can be split
with a 60-mm refractor
at 120×. The image at left
was captured through
a 6-inch f/10 SchmidtCassegrain.

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