Sky and Telescope - November 2018 - 43

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WHEN TO
USE THE MAP

Late Sept
Early Oct
Late Oct
Early Nov
Late Nov

Midnight*
11 p.m.*
10 p.m.*
8 p.m.
7 p.m.

*Daylight-saving time

ere's a pretty puzzle to contemplate: the
maybe-not-actually-a-cluster NGC 7686, in
the far northwestern corner of the constellation
Andromeda. Look for the short arc formed by the
stars Iota (ι), Kappa (κ), and Lambda (λ) Andromedae.
If you follow the arc to the north-northwest, about 3°
past Lambda Andromedae, you'll find NGC 7686.
The first thing you'll see is a bright star with a
slightly dimmer companion. The brighter one is
HD 221246, a 6th-magnitude K-type orange-red
giant, and its unrelated neighbor is HD 221203, an
eighth-magnitude G-type yellow-orange giant. The
two stars lie 900 and 1,300 light-years away, respectively. NGC 7686 lies behind them, about 5,000
light-years away. With a visual magnitude of 5.6, the
cluster is brighter in total than both stars combined,
but its light is spread across ¼°, or half the diameter
of the full Moon. Depending on sky transparency and
your level of dark adaptation, it might take a few minutes for NGC 7686 to swim into view. When it does,
you'll see a halo of faint light centered on HD 221246,
spangled with dimmer stars. Many of those apparent
cluster members are in fact nearby field stars, less
than 100 light-years away.
As for the "cluster," its reality is in doubt. There's
definitely a gaggle of stars lurking out there beyond
HD 221246, but it may just be a chance grouping. Still,
NGC 7686 looks enough like a cluster to have caught
the eyes of generations of professional astronomers,
so we shouldn't feel bad for taking a look. At the very
least, it gives us the opportunity to unpack some
space in our heads while we behold something pretty,
and that's a win in my book.
¢ As much as he wants to understand the structure
of the cosmos, Contributing Editor MATT WEDEL is
still a sucker for a nice view.
sk yandtelescope.com * N OV E M B E R 2 018

43
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Sky and Telescope - November 2018

Table of Contents for the Digital Edition of Sky and Telescope - November 2018
