BINOCULARUNIVERSE
BY PHIL HARRINGTON66 ASTRONOMY • FEBRUARY 2018s the stream of the
winter Milky Way
flows southward
toward the horizon,
it passes through
eastern Orion and Canis Major,
and continues through a region
that looks nearly starless to the
naked eye. Much of this empty
patch of sky belongs to the con-
stellation Puppis.
Puppis is one of three con-
stellations carved from the old
star-picture Argo Navis. Dating
from ancient Greek mythology,
the Argo was the mythical ship
Jason and the Argonauts used
to search for the Golden Fleece.
When viewed from Greece, the
stars of Argo skimmed the
southern horizon, as if the ship
were “sailing” across the
Mediterranean Sea.
French astronomer Nicolas-
Louis de Lacaille (1713–1762)
was the first to dissect Argo
Navis into several components.
In his 1763 catalog of the south-
ern sky, Coelum Australe
Stelliferum, he introduced
Puppis the Stern (or Poop
Deck), Vela the Sails, and
Carina the Keel. Two creatures
were also drawn to accompany
the trio: Columba the Dove andVo l a n s t h e F l y i n g F i s h.
For us living in the Northern
Hemisphere, Puppis is the most
familiar part of Argo Navis.
Truth be told, it offers little to
the eye alone. But thanks to the
Milky Way running through,
the region is rich in deep-sky
treasures. This month, we are
going to seek out an often
ignored winter star cluster, M93.
Unfortunately, since there
are no nearby bright stars to
guide our way, finding M93 can
be a challenge. Because we will
need to bounce from point to
point to point, it will make your
life easier if you can mount
your binoculars to a tripod or
other support. That way, you
won’t need to re-aim each time
you pause along the way.
Begin at Canis Major and
brilliant Sirius (Alpha [α] Canis
Majoris). Trace the Large Dog’s
body southeastward for about
11°, or two binocular fields,
until you get to Wezen (Delta
[δ] CMa). Once centered on
Wezen, look for two 4th-magni-
tude stars in the same field.
They are Omega (ω) CMa to its
southeast and Tau (τ) CMa to its
northeast. Tau is a type O blue
supergiant star, one of the mostluminous stars in tonight’s sky.
Studies show that it is produc-
ing 280,000 times more energy
than our Sun. It lies some
50,000 light-years away.
Take a close look at Tau. Does
it look a little fuzzy to you? It
might, especially if you are using
15x or more. That’s because Tau
is the brightest of several hun-
dred stars in the tight open clus-
ter NGC 2362. Trying to make
out the rest of the bunch is made
difficult by Tau’s overwhelming
brightness. My 10x50s fail, but I
can see a few points through my
16x70s. Aside from Tau, the
brightest cluster stars shine at
7th magnitude.
From Tau and NGC 2362,
look about a binocular field due
east for 3rd-magnitude Xi (ξ)
Puppis and its 5th-magnitude
neighbor, SAO 174592. Both
are spectral type G stars like
our Sun, although they are sig-
nificantly more massive. Their
subtle yellowish tints contrast
nicely against a field of blue-
white stardust, especially if you
slightly defocus the view. But
while they may look close
together, it turns out that this
pairing is just an illusion. Xi is
about 1,350 light-years from
Earth, while its “companion” is
only 300 light-years away.
While admiring Xi, you
should also notice a dim glow
in the same field, just 1.5° to its
northwest. That’s our quest,
open cluster M93. Charles
Messier discovered M93 in
March 1781. He described it as
a “cluster of small stars without
nebulosity.”
Through 50mm binoculars,however, M93 does look nebu-
lous, with about a half-dozen
or so faint points peeking out.
Through my 10x50s, M93
impresses me as triangular in
shape. Switching to my 16x70
and 25x100 giants, I can also
imagine what the famous 19th-
century astronomer William
Henry Smyth (1788–1865)
described in his 1844 classic
Bedford Catalogue as a starfish
when he looked this way. Still
others envision a spider or a
butterf ly.
About 80 stars comprise M93.
The brightest are type B blue
supergiants and shine at 8th
magnitude. Buried within are no
fewer than eight orange and red
giant stars. Can you spot any of
them? The brightest, at 8th mag-
nitude, is just west of center.
But be forewarned that to see
M93, you’ll need to plan your
visit. Its southerly position in
our sky, no more than 27° above
my horizon at 40° north lati-
tude, means that the best view
comes when it’s on or near the
meridian. On February 1, it cul-
minates at about 11 p.m. local
time. By month’s end, that will
occur about two hours earlier.
Have a favorite binocular
target that you’d like to share
with everyone? Tell me about it.
Contact me through my web-
site, philharrington.net.
Until next month, remember
that two eyes are better than
one.Winter star
clusters
Two rich star groups
offer dazzling views.A
Open cluster M93 is a rich, tight grouping of stars that jumps out in a binocular view.The bright but sparse cluster NGC 2362 surrounds 4th-magnitude Tau Canis Majoris.Phil Harrington is a longtime
contributor to Astronomy and
the author of many books.DAN CROWSONADAM BLOCK/MOUNT LEMMON SKYCENTER/UNIVERSITY OF ARIZONA