SOUTHERN
SKY
MARTIN GEORGE describes the solar system’s changing landscape
as it appears in Earth’s southern sky.August 2019: Gas giants galore
The solar system’s two largest
planets continue to grace these
late winter evenings. Jupiter
and Saturn both lie well south
of the celestial equator and
climb high from our part of
the world, providing magni-
ficent views whether you
observe with the naked eye
or with optical aid.
Jupiter appears far more
prominent. The giant world
shines at magnitude –2.3 in
mid-August and passes nearly
overhead as twilight fades to
darkness. Its slightly yellowish
hue contrasts nicely with
nearby Antares, the star that
marks the heart of Scorpius the
Scorpion, which appears one
binocular field above the
planet. Oddly enough, Jupiter
actually lies within the confines
of Ophiuchus, near where the
Serpent-bearer’s southern bor-
der meets the arachnid’s north-
ern side. The planet hardly
budges against the starry back-
drop this month, reaching its
stationary point during
August’s second week.
As dazzling as Jupiter
appears to the naked eye, it
really sizzles when you turn a
telescope in its direction. The
gas giant’s atmosphere resolves
into an alternating series of
bright zones and darker belts
that run parallel to one
another. Finer details emerge
near the borders of these belts
under good seeing conditions.
All this activity plays out on a
disk that measures a healthy 41"
across the equator. You’ll also
want to follow the motions of
Jupiter’s four brightest moons.
Scan 30° to Jupiter’s lower
right and you’ll see Saturn.The ringed planet follows about
two hours behind Jupiter and
thus appears nearly overhead
in midevening. Saturn resides
against the stunning backdrop
of Sagittarius the Archer, not
far from the asterism that our
Northern Hemisphere friends
call the Teapot. The giant world
shines at magnitude 0.2, some
four times brighter than any of
the constellation’s stars.
Especially on nights with
good seeing, Saturn is a superb
telescopic sight. The planet’s
disk measures 18" across at
midmonth while the rings span
41" and tip 25° to our line of
sight. The large tilt provides
excellent views of ring struc-
ture. You should be able to
notice the thin, black arc of the
Cassini Division that separates
the outer A ring from the
brighter B ring.
A waxing gibbous Moon
occults Saturn on August 12.
The event can be seen in a dark
sky from eastern Australia
(except the far southeast), most
of New Zealand’s North Island,
and much of the South Pacific
Ocean. From Sydney, Saturn
disappears behind the dark
limb of the 91-percent-lit Moon
at 8h34m UT and reappears
from behind the bright limb at
9h23m UT. From Auckland,
New Zealand, the correspond-
ing times are 9h16m and
10h16m UT.
You’ll have to wait for morn-
ing twilight to find the Sun’s
smallest planet. Mercury
reaches greatest elongation
August 9, when it lies 19° west
of the Sun and appears 7° high
in the east-northeast a half-hour
before sunrise. The innermostplanet shines at magnitude 0.1
and may be hard to spot with-
out binoculars. A telescope
shows Mercury’s 8"-diameter
disk and crescent phase.
The two planets that orbit
closest to Earth remain lost
in the Sun’s glare all month.
Venus passes on the far side of
the Sun from Earth, a configu-
ration known as superior con-
junction, August 14. It will
return to view low in the west
after sunset in late September.
Slower-moving Mars will be in
conjunction with the Sun in
early September and remains
out of sight until November.The starry sky
Nothing quite compares with
the wonderful view we get of
the starry sky during the early
evening hours at this time of
the year. With the soft glow
of the Milky Way and the
magnificent constellation
Scorpius the Scorpion passing
nearly overhead, Southern
Hemisphere observers have an
unequaled view.
It is sometimes easy to for-
get that Ophiuchus the Serpent-
bearer tucks in neatly beneath
Scorpius. Although this large
star grouping is not one of the
12 official zodiacal constella-
tions, it actually holds a much
longer stretch of the ecliptic
than Scorpius.
On a moonless night away
from the city, take some time
to explore a remarkable area in
the southwestern corner of
Ophiuchus. The region, cen-
tered on the multiple star Rho
(ρ) Ophiuchi, is a favorite of
astroimagers as well. It lies some
3° north-northwest of Antaresin Scorpius and, this month at
least, 6° west of Jupiter.
Under excellent conditions,
binoculars reveal patches of
nebulosity in this area. (To be
truthful, however, it takes a
good image to see them well.)
Rho is embedded in a bluish
ref lection nebula that spans
more than 1°, though this is
one of the more difficult
patches to detect visually.
Some of the most captivating
features of this region are sev-
eral tendrils of dark nebulosity
that run east of Rho. Amateur
astronomers have named one of
the more prominent of these
threads the “Dark River.”
The dark nebulae stand out
because few stars appear within
them. The great astronomer
William Herschel noticed the
lack of stars in this area and
referred to it as a “hole in the
heavens” or “an opening in the
heavens.” This was long before
astronomers realized that such
features are clouds of dust and
cold gas that block our view of
stars beyond.
Although the dark nebulae
are tough to see visually, Rho
Ophiuchi itself is a fine target
through small telescopes. At
first you will see three stars that
form a right-angle triangle. Use
a fairly high magnification and
look closely at the brightest of
this trio, and you’ll notice it to
be a lovely double. The two stars
glow at magnitude 5.1 and mag-
nitude 5.7, and are separated by
about 3". I love the view of this
pair through a 10-centimeter
refractor. Although the other
two stars in the right-angle trio
are also doubles, they are far
harder to split.