http://www.skyandtelescope.com.au 57POSS-II / CALTECH / STSCI / PALOMAR OBSERVATORY
you’ll need to change to a higher-power
eyepiece, because you’re going from
observing an object that’s many degrees
in size to one only 3′ wide. Bernes 148
takes high magnification well. The
nebula is well placed with an arc of four
10th-magnitude stars spread across
its north side at an average of 5′ to 10′
from the nebula. The nebula is involved
more tightly with the 10th-magnitude
variable stars HT and HW Lupi.Of dark nebulae
and globular clusters
A second dark nebula in northern
Lupus can be found just 1° northwest
of 3.4-magnitude Eta (η) Lupi. This is
SL 11, a 30′ region featuring a number
of smaller dark patches. Just south of
the 6.4 magnitude star HD 142889 and
west of HD 143473, these very dark
areas measure about 10′ across. Expert
observer Mel Bartels found this a tough
target, so be patient here. It may help to
edge the brighter stars out of your field
of view before searching for the subtle
contrast between the nebula and the
background Milky Way glow.
Just 2° west of SL 11 you’ll find
the globular cluster NGC 5986. The
proximity of globular clusters to many
dark nebulae led early astronomers
like William Herschel to the erroneous
conclusion that the stars comprising
globular clusters had been swept up
from the dark voids to form a condensed
sphere of brilliance. Today we know this
isn’t true; what had been thought to be
empty voids in space are actually huge
clouds of dust and gas that eventually
are brought together by the effects of
galactic encounters, supernovae and
gravity to form the protostellar regions
of new planetary systems.
NGC 5986 appears grainy through
a small scope, with perhaps two to
three individual stars popping at the
northeastern edge; you’ll need 30 cm of
aperture or more to resolve more than a
few stars.Collar of darkness
Heading farther south along the Wolf’s
neck, we encounter SL 7 about 3½°southofEtaLupi.SL7extends1°in
width and almost 3° in length. The
POSS image above is set on the nebula’s
central region, just off 4.9-magnitude
HD143009,buttheopaquedustcloud
extendsoutofthefieldofviewbothto
the lower right (southwest) to touch
the constellation Norma and to the
upperlefttotagScorpius.You’llneed
arich-fieldtelescopewithawide-angle
eyepiece to get the best look at such a
large cloud.
SL7hasanoverallopacityof
6, offering good contrast with the
skyglow. The darkest section appears
to be the inky black pool southeast
ofHD143009.Thecloudbreakswith
brightness as it extends southwest
andnortheast,butundertheright
conditions,youmaybeabletotraceits
entire length.Onward and eastward
If these fine examples of dark
nebulae aren’t enough, you needn’t
go very far for more first-class targets.
Southern Scorpius lies east of Eta Lupi;
here you’ll find a range of large and
small nebulae with various opacities.
The best is SL 14 (Bernes 149), a
stretch of darkness with a collection
of variable stars, including the
12.4-magnitude T Tauri star HK Lupi.
HK Lupi also boasts a bright nebula
just a bit dimmer than Bernes 148.
While you’re in the area, look for B231
and B233, and for variety, finish up
with HD 149447, a 4.2-magnitude K 5
orange star.RICHARD P. WILDS' latest publication
is Bright and Dark Nebulae: A Pocket
Field Guide (Springer, 2016).STHE VOID You won’t see the twists and turns of dust and clouds shown in deep sky images of
dark nebulae. Instead, you’ll see absence: a dark swath of apparently empty space, free of stars,
free of skyglow. This POSS-II image offers a view closer to what you’ll see through your eyepiece.HD 143009SL 7