Sky & Telescope - September 2021 - 29

SKETCH: HOWARD BANICH; X-RAY: NASA / R. FESEN / MONTHLY
NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 2018
The First Veil - NGC 6960
Let's begin our survey of the Veil
starting with the western side of the
Loop and working eastward. To see
the nebula at its best, a narrowband
eyepiece filter (such as an O III) and
dark, moonless skies are essential.
Bright enough to be a fairly easy
VEIL #1 Finding 52 Cygni should bring
you right to the nebulosity of NGC 6960.
Spend some time identifying the various
arcs that make up this westernmost part of
the Cygnus Loop.
52 Cyg
naked-eye star, 4.2-magnitude
52 Cygni is the perfect place to
start exploring the Cygnus Loop.
No star-hopping or Go To mount
is needed - just look up and point
your scope at the star. If you need
help, start at Epsilon (ε) Cygni, then
drop about 3° due south to find
52 Cygni and the westernmost portion
of the Loop.
The star is seemingly poised just
NGC 6960
off the western edge of nebulosity,
but is only about 200 light-years
away - approximately 12 times
closer than the Loop. Many observers
miss the fact that 52 Cygni is
also a lovely double star, designated
ADS 14259. However, the fainter secondary
star is obscured by an O III
filter. Without a filter, the lovely
soft-yellow primary is offset by its magnitude-8.7 secondary
star 6.4″ due east.
Sometimes called the Witch's Broom, NGC 6960 comprises
curved, elongated wisps that gradually spread apart
toward the southern end. A collection of arcs contributes
to the brightest parts of NGC 6960. There are several short,
relatively bright streamers along the outer western edge that
are fascinating to trace along their overall length and help
give this particular Veil its distinctive character.
The well-defined northern section is bright, thin, and
highly detailed in a big scope, reminiscent of a monochrome
photo. This part of NGC 6960 has fairly bright edges enclosing
thin wisps that can sometimes impart a 3D cylindrical
appearance. When north is down in the eyepiece, it looks
somewhat like an ethereal tornado with 52 Cygni at its top. It
has two radii, one pointed east, the other west.
The southern arcs continue branching out from one
another, promoting the image of an old-fashioned straw
broom, hence its popular moniker. The arcs are also richly
detailed but gradually fade as they reach southward.
Even farther south is an area of vague feathery swirls
and jumbled nebulosity that extends the general curve of
NGC 6960. It takes a good night and some patience to see
these features, but they make up about a third of the total
length of the western side of the Loop. How far you can trace
these faint features depends on the size of your scope and the
quality of the observing conditions.
The Second Veil - Fleming's
Triangle
This section of the Cygnus Loop,
Simeis 3-188, is moving away from
us, which puts it on the far side of the
Loop's expanding bubble. Generally
known as Pickering's Triangle (after
E. C. Pickering, director of the Harvard
College Observatory from 1877
to 1919), it was actually discovered
by Williamina Fleming in 1904 on a
glass photographic plate. At the urging
of his wife, Pickering hired Fleming
in 1879 to do part-time administrative
work at the Observatory, and two
years later she engaged in astronomical
research. It was common practice
at the time for the head honcho to get
the credit for the work of his subordinates,
but Fleming is the undisputed
discoverer, so here I'll refer to it as
Fleming's Triangle.
This area is generally fainter and
less spectacular than the First Veil, but it's still the thirdbrightest
section of the Cygnus Loop. The wispy, northern
triangular area gradually tapers to the south and a long,
curvy, and rather delicate tail extends even farther south. To
me it looks like a kite flying in moonlight.
The eastern side of the northern triangular area is the
brightest and includes some wonderfully intertwined streamers.
Farther south, I enjoy spending time on a strongly curved
streamer in the tail that's seemingly peppered with more than
a dozen faint stars. It's tempting to think the stars give the
impression of nebulosity, but that's not the case here. And
don't overlook several patches of nebulosity floating between
Fleming's Triangle and the First Veil designated [GS55] 222.
They're easy to pass by unless you
deliberately seek them out.
SHOCK WAVES This composite image
of X-ray (blue), ultraviolet (grayish white),
and infrared (dark blue and red) data highlights
how the expanding supernova shock
wave is sculpting the Cygnus Loop as it
encounters pre-existing clouds. It shows
how the Loop is expanding more readily
north and south toward relatively dust-free
areas. Superposed in white is the visual
emission. The bright dot left and slightly
below of center is the Southeastern Knot
that I note in my description of the Fifth Veil
(see the sketch on page 32).
sk yand tele scope .o r g * SEPTEMBER 2021 29
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Sky & Telescope - September 2021

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