Sky & Telescope - September 2021 - 32

Observer's Sketchbook
Studies have shown the Fifth Veil to be slightly closer to us
than the First Veil, and, combined with Fleming's Triangle on
the far side and the Fourth Veil on the near side, we now have
a feel for the 3D arrangement of most of the Cygnus Loop.
The northern half of the Fifth Veil, NGC 6992, looks much
like a curved, twisted rope of nebulous fibers, which become
more distinct as they extend into the area of NGC 6995. A
smidgen farther south, a series of three east-west curvilinear,
ragged wisps look like shattered cirrus clouds. These are a
combination of NGC 6995 and IC 1340 and constitute my
single favorite field of view of the entire Cygnus Loop.
Paralleling the northern edge of NGC 6992 is a series of
small, faint nebulae that arc westward toward the Fourth Veil,
nearly connecting with it near NGC 6979. Faint extensions
along the inner perimeter of NGC 6992 not only make this
region look wider but also slightly more three-dimensional.
South of IC 1340 hangs a faint, puffy extension that's
difficult to see but mimics the general shape and direction
of IC 1340's curvilinear outline. At the base of this area
a wonderful nebulous squiggle projects southward like a
signature flourish.
And now, another surprise. About half a degree south of
that squiggle is an isolated but fairly bright little knot of nebulosity
dubbed the Southeastern Knot. Arguably the most
fascinating bit of the Cygnus Loop, it's remarkable for being
the early stages of the supernova shock wave encountering
a cloud of gas and dust. Associated with a notable source of
X-rays, it's also fairly bright visually. Quite likely this knot
will become considerably larger and brighter in the next few
hundred years or so. Maybe it's just me, but WOW!
All Together Now
Although the various sections of the Loop are amazing to
explore bit by bit with a large telescope, it's rather like examining
an elephant with a magnifying glass. A short-focus
telescope - such as the homemade 8-inch f/3.3 scope I rebuilt
a few years ago (S&T: Sept. 2020, p. 58) - allows one to see the
entire Loop at once. It produces a 3.5° true field of view with a
Notes on Sketching
My original goal was to only make renderings
of the three brightest sections of
the Veil Nebula as seen with my 28-inch
scope from the dark skies of central
Oregon's high desert. I'd observed the
brighter parts of the Loop for 30 years but
never sketched them.
At the start of the project,
I set up three 15 × 16-inch
sketching clipboards to use
at the eyepiece. Then I lightly
traced the outline of the three
brightest sections of the
Cygnus Loop from photographs
so I could depict
32 SEPTEMBER 2021 * SKY & TELESCOPE
VEIL #5 Here we're seeing
one of two approaching
edges of the supernova
remnant. Also, the X-ray
and visual components
of the Southeastern Knot
are close, but not exactly
coincident.
NGC 6992
NGC 6995
IC 1340
Southeastern Knot
25-mm 100° eyepiece. Equipped with an O III filter, it delivered
a spectacular view under the dark skies of central Oregon.
The 3° diameter of the main bubble of the Cygnus Loop
fits beautifully in the 3.5° field of view. This highly rewarding
sight highlights the Loop's just-cracked-egg look due
to the southern area's more spread-out appearance, which
is somewhat misleading, though, because the actual shock
details in their correct places and proportions.
A useful rule of thumb is to draw at
a size that allows the smallest detail to be
clearly shown, hence the large sketching
clipboards.
Combining the individual eyepiece
sketches of all five Veils into one drawing
of the Loop required a
32-inch-square piece of paper.
This allowed me to transfer
all the detail I'd recorded
in my eyepiece sketches to
the finished pencil drawing
without any loss.
I didn't count, but there are
many overlapping fields of
view represented in the finished drawing. It
shows what the entire Cygnus Loop would
look like through my 28-inch scope if it
had a wide enough field of view - or if the
8-inch f/3.3 scope could produce an image
as bright and detailed as the 28-inch.
The two telescopes gave such different
views that I consider them both essential
to the success of the project. Even
though I did all my eyepiece sketching
with the 28-inch, without the 8-inch scope
I wouldn't fully appreciate the impact of
the Cygnus Loop as a single object. It was
the view through the 8-inch that changed
how I think about this beautiful supernova
remnant.
VEIL TEXTURE: NASA / ESA / HUBBLE
HERITAGE TEAM; SKETCH AND ARTIST:
HOWARD BANICH (2)
Sky & Telescope - September 2021

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