My first Magazine Sky & Telescope - 02.2019 | Page 57

N
a narrowband filter. I simply begin by
pointing the scope at a spot one-third of
the way from Theta (θ) to Gamma (γ)
Canis Majoris and then push the scope
east. At 48× with an O III filter, there’s a
roundish glow with a tail that starts at
its southern edge and strikes out toward
the west-southwest. Keeping the O III
filter and boosting the magnification to
102×, the round bubble looks bright-
est along a fat arc that curves north
through west to south so that it and the
tail form a backward numeral 2 in my
mirror-reversed field of view.
NGC 2359 appears more complex
when studied with my 10-inch reflector
at the Winter Star Party. At 70× with an
O III filter, the boldface 2 stands about
6½′ tall and isn’t mirrored. Fainter
extensions proceed east and northwest
from the top of the 2, and another
stretches the 2’s tail westward. The
western extensions stand out better
than the eastern one, and they make
the helmet’s wings or horns. A star
the apparent orbit of Sirius
B with respect to Sirius
A, as projected onto the
plane of the sky. The true
orbit is inclined 43º to the
sky. The dates are for the
beginning of the year.
M50
–10°
θ
2359
–15°
Sirius
γ
ν 3
Sh 2-301
2040
1990
–20°
Orbit of Sirius B
2015
M41
1992
10˝
8˝
6˝
4˝
2˝
2˝
Sirius A
1994
–25°
τ
2˝
ω
2004
1996
2002
2000
1998
ξ 1
CANIS
MAJOR
2362
2008
2006
ο 1
ο 2
h3945
–1
ξ 2
2˝
2012
2010
β
ν 2
4˝
2018
α
ι
6˝
2020
marks each end of the 2’s curve, and
one more sits along the inside edge. A
narrowband fi lter also gives a nice view,
but the brighter parts of the nebula are
obvious even without a fi lter.
The round part of NGC 2359 is a
Wolf-Rayet bubble blown by a fi erce
2035
2025
nebula NGC 2359 (also cataloged as Sharpless
2-298) its evocative shape. Winds from the star
blow through a surrounding molecular cloud,
creating and distorting a nebulous bubble as
they move.
q The fi gure below shows
North
2030
p The massive Wolf-Rayet star WR7 gives the
δ
σ
Much easier quarry dangles 4° south
of Sirius in the guise of Messier 41.
This large open cluster is neatly framed
through the 130-mm scope at 37×, dis-
playing 50 bright to faint stars penned
into 40′. The stars are most concen-
trated within the group’s central 15′, a
region embellished with several colorful
stars. The most prominent include the
two bright stars near the center, yellow-
orange and yellow, and three slightly
dimmer golden stars that enclose the
pair in a 13.5′-tall triangle, its pointy
end in the north. The cluster is quite
beautiful in the 10-inch scope at 44×. It
gleams with more than 100 stars, many
in raggedy chains splayed outward from
the center.
M41 is an intermediate-age open
cluster, 240 million years old, parked
2,300 light-years away from us. Accord-
ing to recent papers, members cover a
diameter of about 1½° on the sky and
conservatively total about 880 solar
masses.
Our next target is the emission
nebula NGC 2359, popularly known
as Thor’s Helmet for its resemblance to
the Norse god’s apocryphal headgear,
variously depicted as having wings
or horns. From home, Thor’s nebula
is easily spotted in a 23× sweep with
the 130-mm refractor and the aid of
ε
4˝
–30°
0
1
2
3
4
5
6
7
ζ
η
South
7 h 30 m
7 h 00 m
κ
6 h 30 m
sk yandtele scope.com • FE B RUA RY 2 019
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