Sky and Telescope - August 2018 - 54

Berkeley 53

AUGUST 2018 OBSERVING
Deep-Sky Wonders by Sue French

Espin 999

NGC 7031

HD 199955

Cygnus
Puzzlers
Get to know these
deep-sky strangers
this summer.

Sh 2-120

Sh 2-121

AUGUST 2 018 * SK Y & TELESCOPE

p The diffuse emission nebulae Sh 2-120 and
Sh 2-121 are subtle glows ensconced in the
dust clouds at the periphery of the Le Gentil 3
dark nebula complex in northeastern Cygnus.
NGC 7031, described by Steve Gottlieb as "not
very rich" and "fairly scattered," shows about
two dozen stars in larger scopes.

The nebula ﬁnally suggests a Lilliputian disk at 299×. It's the brightest and
northernmost object in a 40″-long arc
it makes with two dim stars. The arc
is shown in my second drawing with
respect to 9th- and 10th-magnitude
stars (labeled 3 and 2 respectively) 3.8′
apart and east of the nebula.
According to a 2011 study published
in the Astronomical Journal by Raghvendra Sahai and colleagues, given a distance of 15,500 light-years, we are now
seeing NGC 6833 at a time when it had
been expanding for little more than 700
years, one reason it appears so petite.
A horse of a different color, the
elderly open cluster Berkeley 53 is
about 1 billion years old. It sits 2.3°
east-northeast of 51 Cygni and clasps
the 6.6-magnitude star HD 199578
within its eastern boundary. Aiming my 15-inch reﬂector at the area,
there's an interesting oval ring of fairly
bright stars with HD 199578 mark-

ing its eastern end - but that's not the
cluster. Look instead for a faint glow
cozied up to the bright star. At 247× its
haze spans roughly 5′. It contains some
obvious foreground stars, the brightest
one orange, and at least 15 very faint
to exceptionally faint stars, perhaps
a few of which might reach the feeble

3
2

p Top: This sketch shows the field around the
planetary nebula NGC 6833 as viewed through
a 130-mm refractor at 117×. An O III filter will
help you pull the nebula, marked here with
an arrow, out of the stars. Bottom: Greater
aperture and more magnification make NGC
6833 more apparent. Look for it at the top of a
40″-long arc west of the 10th-magnitude stars
marked 2 and 3 here.

SK E TCHES: SUE FRENCH; CYG NUS: R AUL VILL AV ERDE

he plentiful deep sky holds many
wonders you've never heard of, or
perhaps could never quite ﬁgure out.
Some aren't what they seem, are difﬁcult to pinpoint, or have an indeﬁnite
status. Let's scoop up a handful of these
curious little stumpers and see what we
can make of them.
We'll begin with the tiny planetary nebula NGC 6833. Since it isn't
signposted by any bright stars, those
without computerized telescopes will
need to star-hop, with the aid of a good
atlas, from the closest star they can see.
With a diameter of only 1″, the nebula
is quite difﬁcult to distinguish from
the stars. A 10.6′-long star pattern near
the planetary can help you pick out the
nebula, shown on my sketch as seen
with a 130-mm refractor. Its brightest
stars are 9th-magnitude. Using a magniﬁcation of 117× and an O III ﬁlter,
the identity of the planetary becomes
apparent. The stars dim, and NGC 6833
becomes brighter than the stars labeled
1 and 2. On a night of very good seeing,
my 10-inch reﬂector makes a better job
of it. Even at 88× NGC 6833 gives itself
away by its bluish color, and at 187× it
looks suspiciously edged rather than
showing a sharp point like the stars.

Sky and Telescope - August 2018

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