Sky & Telescope - USA (2019-08)

6709

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HD 172827

HD 172744

HD 171975

WHEN TO

USE THE MAP

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Early July Midnight*

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Late Aug Dusk

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  4
  Binocular Highlight by Mathew Wedel
  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 some-
  times 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 fi ne,
  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 givesMATT WEDELmany
  opportunities to learn the difference between look-
  ing and seeing.
  Something for
  Everyone
  skyandtelescope.com • AUGUST 2019 43