Sky and Telescope - December 2015 - 33

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M41

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M41

I made these observations from my backyard in
eastern Los Angeles County, using 15×70 binoculars with
a 4.4° ﬁeld of view. Most of the objects we'll visit on this
tour are also visible in smaller instruments, especially if
they're mounted on a tripod or braced against something
sturdy. Equally important for rewarding binocular observing is good dark adaptation. If I pull the hood of my jacket
up around my face to block out any incidental light, I'm
able to go deeper and see more, even in suburban skies.
Sirius, the most spectacular jewel in the southern
skies for Northern Hemisphere observers, makes a good
anchor and starting point (Stop 1 on the map on page
32). From Sirius, move directly south about four degrees
to ﬁnd M41, one of the brightest open clusters in the
winter skies (Stop 2). Before you move on, notice how
the brighter stars in the cluster form a pair of concentric
curls like breaking waves.
Another 4° slide to the east-southeast will bring you to
Collinder 121 (Cr 121), a loose association dominated by
Omicron1 (ο1) Canis Majoris (Stop 3). Evidence is mounting that the brighter O and B stars in this ﬁeld are separate from the open cluster, which lies about 3,500 lightyears away. Omicron1 itself is also fairly distant, at nearly
2,000 light-years, but as an orange, K-type supergiant it's
incredibly luminous. The complexity of the view here iss
a useful reminder that space has depth - we don't look
k
at the night sky so much as into it.
Our gentle arc to the east continues with a third 4°
hop, southeast from Omicron1 to the much brighter Deltaa
(δ) Canis Majoris, also known as Wezen (Stop 4). This
is another big, young supergiant, and we'll use it as a
base camp for a little side trip. Start by taking in the arc
of bright stars east of Delta, which forms a miniature
"corona" asterism about 2° across. The brightest star in
the arc is Omega (ω) Canis Majoris. Omega is a variable
star, normally a modest magnitude 4.1 but occasionally
brightening up to 3.6. The change in brightness is caused
not by the star itself, apparently, but by the formation,
outburst, and dissipation of a circumstellar disk.
About 2° north-northeast of Omega is a pair of bright
stars oriented north-to-south: 29 Canis Majoris to the

JER E

CMa

ED U

2 First catalogued in the mid-17th century by Giovanni
Batista Hodierna, open cluster M41 is visible to the naked
eye in dark skies. With 15×45 image-stabilized binoculars, you
should be able to resolve some 30 stars.
4 5 6 Use Delta Canis Majoris as a waymarker on the
path to Omega, Tau, and 29 CMa. Eta lies approximately 5°° to
the southeast of your waymark.
north, and Tau (τ) Canis Majoris below (Stop 5). Take
a close look at Tau. If you're under good skies, you may
catch a glimpse of the open cluster NGC 2362 (Caldwell
64) as a faint wisp of light surrounding the brighter star.
Or rather, brighter stars: Tau is actually a stellar system
of four giant stars in a tight gravitational bear hug, plus
a single smaller star, probably captured, that lies 13,000
a.u. from the rest.
Another beautiful double awaits you just over 1°
north-northwest of the 29-Tau pair. This is Herschel
3945 (h3945), the "Winter Albireo." Some observers
report splitting the beautiful blue and gold components
with 10×50 binoculars, but I have to go up to the 15×70s,
braced very securely, to get a clean split. Give it a shot
and see what works for you.
Now go back to bright Delta and shoot through the

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Sky and Telescope - December 2015

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