SOUTHERN SKY
December 2019
Say farewell to the gas giants
December begins with
a fine view of three
bright planets strung across
the early evening sky. Jupiter
anchors this impressive gather-
ing from its perch in western
Sagittarius the Archer.
Although twilight surrounds
the gas giant world, it stands
out because it shines brightly
at magnitude –1.8.
Unfortunately, the show
doesn’t last long. Jupiter sinks
closer to the Sun’s glow with
each passing day and becomes
lost in the glare during
December’s second week on its
way toward solar conjunction
on the 27th. The planet’s low
altitude means its light passes
through thick layers of Earth’s
atmosphere, so it doesn’t look
impressive through a telescope.
Venus appears much more
prominent. Our neighboring
planet shines at magnitude –3.9
and stands out like an air-
plane’s landing light. Venus
starts the month one binocular
field to Jupiter’s upper right
and within 1° of Lambda (λ)
Sagittarii, the 3rd-magnitude
star that marks the top of
Sagittarius’ Teapot asterism.
Un li ke Jupiter, however,
Venus draws away from the
Sun during December. At
month’s end, it resides in cen-
tral Capricornus and sets two
hours after our star. When
viewed through a telescope, it
then shows a disk that mea-
sures 13" across and appears
distinctly gibbous.
Returning to the twilight
scene in early December,Saturn marks the top end of
the pretty planetary lineup. You
can find it glowing at magni-
tude 0.6 against the backdrop
of eastern Sagittarius some 11°
to Venus’ upper right. Like
Jupiter, Saturn pulls closer to
the Sun this month and gets
swallowed by the twilight. As
it drops lower, it passes near
Venus heading in the opposite
direction. The two planets
slide within 2° of each other
December 11.
You can still get a decent
view of Saturn through a tele-
scope early this month. On the
1st, the planet’s globe appears
15" across while the ring system
spans 35" and tilts 24° to our
line of sight.
Two other planets lurk in
the early morning sky. Mars is
easy to spot in the east before
dawn, particularly later in the
month as it climbs into a dark
sky. Although the magnitude
1.6 planet is not prominent, it
does outshine the background
stars of Libra the Scales. A tele-
scope reveals a featureless disk
that spans just 4".
Mercury poses more of a
challenge. You might glimpse
it some 5° high in the east-
southeast a half-hour before the
Sun rises in early December.
Look for its magnitude –0.6
glow through binoculars.
An annular solar eclipse
occurs December 26. Although
the path of annularity — the
narrow track on Earth’s sur-
face where the Moon passes
directly in front of the Sun and
leaves a sunlit ring around itssilhouette — resides solely in
the Northern Hemisphere, it
does dip within 1° of the equa-
tor. This means people across
a wide area of the Southern
Hemisphere, including most
of northern and western
Australia, can see a partial
eclipse. From Darwin, the
eclipse lasts from 5h14m to
7h42m UT, and the Moon
obscures 31 percent of the
Sun’s area at maximum. As
with any non-total eclipse, be
sure to protect your eyes by
viewing only though a safe
solar filter.The starry sky
Astronomers officially divided
the sky into 88 constellations
about a century ago. Many
depict figures, creatures, or
objects that skywatchers
throughout the ages have
wanted to commemorate.
Unfortunately, only a relative
handful of these star groups
come close to resembling the
subject they are meant to
celebrate.
But many asterisms — col-
lections of stars within a con-
stellation or spanning multiple
constellations — really do look
like their namesakes. For
example, Southern Hemisphere
observers refer to Orion’s Belt
and several stars to its south as
the Iron Pot or Saucepan.
To me, one of the most
striking asterisms is a giant
pattern that strongly resembles
the Greek letter epsilon (ε). The
figure spans 1 hour 20 minutes
of right ascension and 35° ofdeclination and comprises stars
belonging to the constellations
Eridanus the River and Fornax
the Furnace. This region passes
nearly overhead after darkness
falls on December evenings.
And for what it’s worth, I find
it easier to see the epsilon by
gazing at the real night sky
rather than at a star chart.
It’s easiest to start at Gamma
(γ) Eridani, which marks the
asterism’s southeastern end. To
continue the pattern, shift your
gaze to the west (left). The
lower half of the epsilon follows
the curve of the River clock-
wise, with the letter’s central
bar formed by the nine stars
Tau^1 (τ^1 ) to Tau^9 (τ^9 ) Eri.
Now return to Tau^3. The
epsilon’s upper left section
traces a path from there across
Fornax, picking up Gamma^2
and Beta (β) Fornacis, the
Furnace’s three tightly grouped
Eta (η) stars, and then diving
back into the River to Theta (θ)
Eri. When viewed through a
telescope, Theta proves to be
a delightful double star with
magnitude 3.4 and magnitude
4.5 stars separated by 8.3".
Finally, the asterism’s top
section curves more to the east
(right) and ends with the three
stars h, g, and i Eri. While
you’re snaking through this
area, sidetrack a bit to the north
and locate Chi^1 (χ^1 ), Chi^2 (χ^2 ),
and Chi^3 (χ^3 ) For. A telescope
delivers wonderful views of
two nearby spiral galaxies:
NGC 1316 just to these stars’
southwest and NGC 1365 to
their east.