Page 60 - BBC Sky at Night - September 2017 UK

60 SEPTEMBER THE SKY GUIDE

STEPHEN TONKIN’S runs northeast-southwest before curving east and
passing 1° west of 27 Aquilae. The eastern edge
BINOCULAR TOUR is quite distinct, but the transition to the Milky Way
background is more diffuse to the west. SEEN IT
September offers a debated globular, a dark 5 THE COATHANGER
lizard and the delight of a famous asterism 10 x We now head north to a popular
50 star-party piece, an asterism variously
designated Collinder 399, Brocchi’s Cluster and

Tick the box when you’ve seen each one therefore older. It is an intermediate age cluster Al-Sufi’s Cluster. Find it 5° south of mag. +4.4
at just under 700 million years old. SEEN IT Anser (Alpha (_) Vulpeculae) or 4° northwest
1 THE SUMMER BEEHIVE of mag. +4.4 Sham (Alpha (_) Sagittae). Even
10 x Our first target’s brighter stars form the 3 GRAFF’S CLUSTER small binoculars will reveal the 10 brightest
50 word ‘HI’. Locate mag. +2.7 Cebalrai 10 x Pan 3° from NGC 6633, in the direction stars that give this asterism its common name.
(Beta (`) Ophiuchi) and you will see IC 4665, 50 of mag. +4.6 Alya (Theta (e) Serpentis), It spans 1.5°, which means that it will stay within
the Summer Beehive, in the same field of view. where you will find a misty patch just over 1° the field of view long enough for several
It’s just over 1° northeast of the star. You should in diameter. This is Graff’s Cluster, IC 4756, an consecutive star-party observers to see it in
be able to resolve a dozen or so stars with a enormous grouping of stars over 20 lightyears mounted binoculars. It was first recorded by
pair of 10x50s, including the curved chain of across and approximately 1,300 lightyears away. the 10th Century Persian astronomer Abd
hot white stars that forms part of the letter H. It richly rewards patience: try averted vision on al-Rahman al-Sufi. SEEN IT
This is a relatively young cluster, being less it. As more detail comes into view, you may
than 40 million years old. SEEN IT experience what others have described as being 6 M71
“brighter stars, scattered over a background of 15 x Is M71 a tight open cluster or a loose
2 NGC 6633 diamond dust”. Its yellow stars suggest that it is 70 globular? After decades of dispute, the
10 x From IC 4665 navigate 10° eastwards, a similar age to NGC 6633. SEEN IT consensus is that it is the latter. You can find this
50 where you will find NGC 6633. This enigmatic object just south of the mid-point of a
lovely little cluster is often overlooked in lists of 4 BARNARD 138 line joining mag. +4.3 Delta (b) and mag. +3.5
binocular objects because it can be tricky to 10 x You will need a transparent dark sky for Gamma (a) Sagittae. M71 is quite faint at mag.
find, but it is easily visible in a pair of 10x50s, 50 our next object, Barnard 138, or Barnard’s +8.2, but 15x magnification should at least reveal
the four brightest stars shining against the Black Lizard. Identify mag. +3.4 Delta (b) Aquilae that it is not a star and averted vision will confirm
20-arcminute elongated glow of unresolved and navigate 2.5° southwest to mag. +5.2 23 this. The cluster spans 27 lightyears and is
fainter stars. Compare it to the Summer Beehive Aquilae. Let your eyes to settle and you should 12,000 light years away from us. It’s about
and you will see that its stars are yellower, and see that this star is in a narrow dark band that nine billion years old. SEEN IT

M27 _ VULPECULA
a Anser
_ a SAGITTA k
b j
` M71 b +
_ 5
6
DELPHINUS Sham Collinder 399
¡ `
HERCULES

a ¡
Tarazed c
Altair
_
Alshain
`
+

Rasalhague _
2
d b e NGC 6633
Alya IC 4756 NGC 6572
23 3 1

27 IC 4665
AQUILA B138
4 `
5° N a Cebalrai
SERPENS
E h SCUTUM OPHIUCHUS
CAPRICORNUS CAUDA
_ W ` Collinder 350
S M11 d

` b

skyatnightmagazine.com 2017