Sky & Telescope - August 2019 - 43

HERCULES

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Binocular Highlight
by Mathew Wedel

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WHEN TO
USE THE MAP

Late June
Early July
Late July
Early Aug
Late Aug

1 a.m.*
Midnight*
11 p.m.*
10 p.m.*
Dusk

*Daylight-saving time

O

ne of my favorite objects in the summer Milky
Way is the open cluster NGC 6709. It lies close
to the western border of Aquila, the Eagle, almost
exactly 5° southwest of Zeta (ζ) Aquilae. From our
vantage point, the cluster is perched just on the edge
of the Cygnus Rift, the great lane of dark dust clouds
that stretches from the celestial Swan to the galactic
center in Sagittarius, the Archer. For once, this isn't
a coincidental alignment; at 3,500 light-years from
us, NGC 6709 is at approximately the same distance
as the vast dust clouds that make up the rift. With a
diameter of a little less than 15 light-years, the cluster
therefore serves as a visual yardstick, allowing us to
appreciate just how breathtakingly colossal are the
large-scale structures of our galaxy.
I also like NGC 6709 for another reason: It's pretty.
Suspended as it is between the brighter lights of
Cygnus and Sagittarius, I think NGC 6709 is sometimes overlooked. But it's well worth a visit. Not only
is the cluster a charming object in its own right, it's
the focal point of a neat binocular asterism. Fanning
about 3° west-northwest from NGC 6709 is a thin
wedge, densely packed with stars, that looks a bit like
the tail of a comet streaming away from the cluster.
This comet tail is bookended at its corners by a pair of
nice binocular doubles: HD 172827 and HD 172744
on the northeast, and HD 171975 and HD 172010
on the southwest. The cluster itself holds some fine,
if challenging, stars, including a pair of red giants on
its southeast margin. NGC 6709 has a little something
for everyone - go see what it has for you.
¢ Binocular observing gives MATT WEDEL many
opportunities to learn the difference between looking and seeing.
sk yandtele scope.com * AUGU S T 2 019

43
http://www.skyandtelescope.com
Sky & Telescope - August 2019

Table of Contents for the Digital Edition of Sky & Telescope - August 2019
