SOUTHERN
SKY
MARTIN GEORGE describes the solar system’s changing landscape
as it appears in Earth’s southern sky.
August 2018: An evening extravaganza
Four bright planets stretch
across August’s evening sky.
Venus lies farthest west, shin-
ing brilliantly against the back-
ground stars of Virgo. On the
1st, it appears 30° below 1st-
magnitude Spica, the Virgin’s
luminary. The magnitude –4.3
planet outshines the star by
some 100 times.
Venus moves eastward
against the starry backdrop
during August. It reaches great-
est solar elongation on the 17th,
when it appears 46° east of our
star and stands more than 30°
high an hour after sundown.
The planet remains the sky’s
brightest point of light until it
sets shortly after 9 p.m. local
time. By month’s end, Venus
pulls within 1.5° of Spica.
The planet’s appearance
through a telescope changes
noticeably throughout August.
On the 1st, it shows a slightly
gibbous phase on a disk that
spans 20". At midmonth, the
Sun illuminates precisely half of
Venus’ 24"-diameter disk. And
by the time August closes, the
planet swells to 29" across while
its phase dwindles to a crescent.
Next in line is Jupiter. The
giant planet stands high in the
northwest as darkness falls,
residing among the relatively
dim stars of the constellation
Libra. Jupiter shines at magni-
tude –2.0, barely one-tenth as
bright as Venus but still notice-
ably brighter than any star.
The gas giant’s atmosphere
provides a visual treat through
any telescope. Look for two par-
allel dark belts, one on either
side of a much brighter zone
coinciding with the planet’s
36"-diameter equator. Smaller
features along the edges of these
belts show up during moments
of good seeing. You can also
track the movements of Jupiter’s
four largest moons over the
course of a few hours.
If you trace a line from
Venus to Jupiter and extend it
a bit farther than the distance
between those two, your eyes
will fall on magnitude 0.3
Saturn. The ringed planet
resides in Sagittarius and
appears high in the sky
throughout the evening hours.
(From a wide swath of the
Southern Hemisphere, it passes
nearly overhead at its peak.)
Saturn moves slowly westward,
or retrograde, relative to the
background stars as Earth
continues to outpace it in the
months following opposition.
Although Saturn is the dim-
mest of the four evening plan-
ets, it is also the most beautiful
through a telescope. And its
great altitude on August eve-
nings provides nearly perfect
viewing conditions. At mid-
month, the planet’s disk mea-
sures 18" across while the rings
span 40" and tilt 27° to our line
of sight. Any scope should
reveal the broad Cassini
Division that separates the
outer A Ring from the brighter
B ring. The narrow Encke Gap
near the A ring’s outer edge
shows up under excellent con-
ditions with a 20-centimeter or
larger instrument.
Head one constellation far-
ther east and you can’t miss
Mars. Only the Moon and
Ve nu s o u t s h i n e M a r s t h i s
month, and neither has the
Red Planet’s distinctive color.
Mars spends most of August in
southwestern Capricornus, but
its retrograde motion carries it
into far eastern Sagittarius in
the month’s final week.
The ruddy world reached
opposition and peak visibility
in late July, and it remains a
stunning sight throughout
August. Although it dims from
magnitude –2.8 to –2.1 and its
apparent diameter shrinks
from 24" to 21", these values
still exceed a typical martian
opposition. And its high eve-
ning altitude promises good
seeing conditions for viewing
fine detail through a telescope.
Mercury proves to be a dif-
ficult target during August.
The innermost planet passes
between the Sun and Earth
on August 9 and then slowly
climbs into view low in the
east-northeast before dawn.
Still, even at greatest western
elongation on the 26th, it
appears only 4° high a half-
hour before sunrise.
The starry sky
The southern sky contains
enough telescopic delights to
keep an observer busy for a life-
time. Even something as small
as a 20-cm instrument will let
you observe a huge number of
these deep-sky wonders.
In winter and early spring,
we reap the benefits of living
in the Southern Hemisphere.
In early evening, the spec-
tacular southern Milky Way
stretches across the sky while
the center of our galaxy passes
nearly overhead.
One of winter’s most famil-
iar star patterns is Scorpius the
Scorpion. The constellation
does resemble a scorpion,
though some see a reversed
question mark in its form. Its
most distinctive features are
1st-magnitude Antares, the star
that marks the Scorpion’s heart,
and the arachnid’s curved tail.
The arc of the tail encloses a
fascinating deep-sky object.
The Bug Nebula (NGC 6302)
lies near the center of the tail,
4° due west of magnitude 1.6
Shaula (Lambda [λ] Scorpii),
the bright star marking the
Scorpion’s Stinger. The Bug is a
planetary nebula, but the word
“planetary” is a misnomer —
such nebulae have nothing to
do with planets. They are the
glowing embers of material
ejected by aging Sun-like stars.
They got their name because
early observers saw a superficial
resemblance to the blue-green
glow of the planet Uranus.
The Bug Nebula looks spec-
tacular through a 20-cm tele-
scope, though smaller apertures
do show it. It is rather small,
spanning 50", but has a high
surface brightness and thus
shows up quite easily. The neb-
ula appears elongated and has a
bright center. You won’t see the
central star that puffed off
these wispy tendrils, however.
Astronomers finally detected
this ultrahot star, which has a
surface temperature of about
200,000 K, with the Hubble
Space Telescope in 2009.
Although photographs show
the Bug’s complexity, its overall
appearance is reminiscent of a
f lying insect with a large wing-
span. Every time I gaze at this
object, however, it reminds me
more of an unfortunate bug
that met an untimely end on
the windscreen of my car.