My first Magazine Sky & Telescope - 02.2019 | Page 56

FEBRUARY 2019 OBSERVING
Deep-Sky Wonders by Sue French
The Dog Star’s Realm
The brilliant beacon of winter leads us to wonderful things.
When wooded knoll is white with snow
And Boreas’s breezes blow,
When early fades Sol’s afterglow,
Resplendent, scintillating low,
The winter’s dogstar beams.
Unrivalled, solitary, bright
As brilliant beacon’s blazing light
Or diamond in the dome of night,
Resplendent and transcendent sight,
The evening’s dogstar gleams.
— Charles Nevers Holmes,
Canicula, 1918
s the brightest star in the night
sky, the Dog Star immediately
draws the eye whenever it graces the
heavens. This brilliant beacon doesn’t
journey alone through space. Although
variations in the motion of Sirius led
Friedrich Bessel to propose a companion
star in 1844, it remained unseen until
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famed telescope-maker Alvan Clark
noticed it while using Sirius to test a
new 18.5-inch lens in 1862. Our Dog
Star’s little companion is affectionately
known as the Pup.
You won’t need an 18.5-inch scope
to see the Pup, but you’ll certainly need
good seeing: atmospheric steadiness,
as well as a scope that’s at the outdoor
temperature and not aimed above heat-
emitting objects such as roofs or pave-
ment. At my home, Sirius is low in the
sky and rarely offers the atmospheric
calm I often enjoy with objects at
greater altitudes, so I’ve confined most
of my Pup quests to times at the Winter
Star Party in the Florida Keys.
My most recent successes came with
my 130-mm refractor and 10-inch
reflector. In the refractor at 273×, the
8.4-magnitude Pup looked faint next
to blazing Sirius, but it stood out much
better on steadier nights through
the reflector at 299× and 427×. High
magnifications are required to pull the
Pup away from the overwhelming glare
of Sirius. The Pup is one of the few
white dwarf stars visible to the average
backyard scope. If you manage to nab it,
keep in mind that the Pup is approxi-
mately the mass of our Sun, yet only
90% as big across as the Earth. Its big
brother Sirius is about twice the mass
of our Sun and 1.7 times as big across,
sparkling at us from a neighborly dis-
tance of 8.6 light-years.
If you’ve never seen the Pup, this is
a good time to start looking. Follow-
ing their 50.1-year orbit, the stars are
currently 11.09″ apart, with the Pup
east-northeast of Sirius. To determine
direction, let Sirius drift from the
center to the edge of your field of view.
The direction of the motion is west;
therefore, the Pup will be nearly on the
opposite side of Sirius. The separation
is widening and will be at its maximum
of 11.33″ from early 2022 to mid-2023,
and then it will narrow toward a mini-
mum of 2.54″ in 2043.
Several observers indepen-
dently discovered the open
cluster M41, including Giovanni
Hodierna (before 1654), John
Flamsteed (1702), Le Gentil
(1749), and fi nally Charles
Messier (1765). The cluster has
about 100 member stars.