Sky & Telescope - October 2022 - 25

SEAN WALKER / S&T
174× revealed several narrow grey ribbons crossing the Swan's
body and lower neck diagonally. I also could see the dense
dust cloud that shapes the Swan's neck, which looks distinctly
darker than any other area in the field of view. There was also
faint nebulosity north of the swan. The associated open cluster
is poorly concentrated and contributes little to the scene.
On the best night at the 1994 Mount Kobau Star Party,
veteran observer John Casino's 36-inch Dobsonian with an
O III filter showed the linear absorption nebulae in the Swan
just as clearly as the photographs of the day.
The Lagoon Nebula (M8), one of the brightest naked-eye
objects in the summer Milky Way, was likely known since
antiquity, and so nobody should be credited as its discoverer.
My 8-inch at 61× and 116× reveals the prominent curving
dark channel between M8's two main lobes, the tiny Hourglass
(the brightest patch of nebulosity within the Lagoon
3′ west-southwest of 9 Sagittarii), and about 40 stars in the
loose open cluster that was born within the nebula. The earliest
spectral type of the cluster stars is O5, implying that it's
only about 2 million years old.
One of the best views I've had of the Lagoon was at Chaco
Culture National Historical Park, located in a very dark corner
of northern New Mexico. In " Diving into the Lagoon " (S&T:
July 2012, p. 61), I describe my explorations of the nebula
with Chaco Observatory's 25-inch Dob, using an O III filter.
At 226× I saw a bright filament in the main dark channel,
along its northwest bank and parallel to it. Even at that power
I noted no more than a vague suggestion of the Hourglass's
shape. I conducted the rest of my survey at 113×. I describe 15
dust clouds within the Lagoon, and I suggest that you hunt
down the three dark nebulae that E. E. Barnard cataloged (as
shown at left). Finding Burnham's Dark Comet was the main
reason that I slewed the 25-inch onto the Lagoon Nebula.
The discovery of the Trifid Nebula (M20) is attributed
to Charles Messier in 1764, although that's rather generous
since he only saw stars. It was, in fact, William Herschel who
discovered it 20 years later.
I see the celebrated dark lanes (B85) of the Trifid Nebula
well in my 8-inch at moderate power, radiating from near
the central triple star (the O8 lucida, HD 164492, powers the
emission nebula). Large apertures make it a quadruple star.
C. E. Barns, in his 1929 book 1,001 Celestial Wonders, captured
the essence of the Trifid: " Bulbous image trisected with
dark rifts of interposing opaque dust-clouds . . . " However,
both my telescope and photographs show four dark lanes, not
three. The 8-inch at 60× also bagged the fainter reflection
nebula to the north.
The Best of the Rest
Messier and fellow French astronomer Antoine Darquier de
Pellepoix independently discovered the Ring Nebula (M57)
in 1779 (see page 41). You'll find it in Lyra, approximately
halfway between Beta (β) and Gamma (γ) Lyrae. It looks like
a smoke ring even in a 60-mm refractor. My 8-inch at 116×
shows M57 as oval, fainter at the ends, and noticeably brighter
CELESTIAL ROSE Sitting in northern Monoceros, in the middle of
a triangle formed by Epsilon (ε), 13, and 18 Monocerotis, the Rosette
Nebula cradles the open cluster NGC 2244. Note that 12 Monocerotis,
the most obvious star on the southeastern edge of the cluster, isn't a
true member but instead is a foreground star.
inside the ring than outside. There's a bright southeastern rim
in my 16-inch at 261×, and on nights with excellent seeing I
can glimpse the 15.7-magnitude central star at 366×.
At the 1990 Mount Kobau Star Party, Casino's 36-inch at
420× revealed a second star within the ring, plus one superposed
on the nebula itself. Then, in a flash of superb seeing,
I discerned broad parallel banding in the gauzy nebulosity
inside the annulus. The banding's momentary appearance
on a sterling night provided me with a lifetime memory.
Apparently, William Parsons, the Third Earl of Rosse, had
previously observed this with his 72-inch Leviathan reflector.
My club's (the Royal Astronomical Society of Canada Okanagan
Centre) 25-inch Dobsonian, at 317× showed the galaxy
IC 1296 only 4′ west-northwest of the Ring.
While comet-hunting in 1865, Lewis Swift chanced upon
the Rosette Nebula (NGC 2237+) in Monoceros. My 7×50
binoculars reveal a formless glow around the central hole
blown by the associated open cluster NGC 2244's young
stars. Don't be fooled by the brightest star, yellow 12 Monoceros:
It's a foreground object. The 4.8-magnitude cluster is
obvious with the naked eye.
With my 16-inch the nebula formed a complete annulus
at 65×, but I discerned no details without a filter. The Rosette
comes alive with an Ultra High Contrast (UHC) filter: At
141× the southern side of the Rosette is the faintest, followed
by the eastern side - but I see four bands of nebulosity, separated
by dark lanes. The northern section is the brightest, and
I note Y-shaped dark lanes there - these are chains of starforming
dark Bok globules (though the individual globules
are hard to detect). On the northwestern to western sides of
the nebula, dark lanes cut through in four places. The dark
lanes due west are very prominent.
sk yand tele scope .o r g * OCTOBER 2022 25
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Sky & Telescope - October 2022

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