SOUTHERN
SKY
MARTIN GEORGE describes the solar system’s changing landscape
as it appears in Earth’s southern sky.March 2018: The evening planets return
The early evening sky has been
devoid of bright planets all
summer, but that comes to an
end as autumn approaches.
Unfortunately, the first two
solar system residents to appear
at dusk don’t climb very high in
March, particularly from more
southerly latitudes. Blame the
shallow angle of the ecliptic —
the apparent path of the Sun
across the sky that the planets
closely follow — to the western
horizon after sunset at this
time of year. A planet’s elonga-
tion from the Sun translates
more into distance along the
horizon and less into altitude.
Venus makes the better
appearance. In late March, it
lies 20° east of the Sun, and
from mid-southern latitudes, it
appears 4° above the western
horizon a half-hour after sun-
set. (Conditions improve closer
to the equator. From Darwin,
Australia, for example, the
planet appears twice as high at
the same time.) Venus shines
brilliantly, at magnitude –3.9,
and should show up clearly in
the twilight if you have an
unobstructed horizon.
Mercury doesn’t fare as
well. The best time to look for
the innermost planet is when it
reaches greatest elongation
March 15. It then lies 18° east
of the Sun but climbs just 1°
high a half-hour after sundown
for those at mid-southern lati-
tudes. (Observers in Darwin
see Mercury at an altitude of
5°.) You’ll need binoculars to
pick up the planet’s magnitude
–0.4 glow.
If these early evening views
leave you unimpressed, just
wait a few hours. Jupiter risesaround 10 p.m. local time in
early March and some two
hours earlier by month’s end.
The planet appears nearly sta-
tionary against the backdrop of
central Libra the Scales. Jupiter
brightens from magnitude –2.2
to –2.4 during March, which
makes it 100 times brighter
than Libra’s luminary, which
glows at magnitude 2.6.
The view of Jupiter through
a telescope is no less impres-
sive. The giant planet’s equato-
rial diameter swells from 39" to
43" during March, delivering
exquisite eyepiece images in
any instrument. Look for an
alternating series of bright
zones and darker belts, perhaps
punctuated by the ruddy cloud
tops of the Great Red Spot, if it
happens to be on the Earth-
facing hemisphere. Your sharp-
est views will come as Jupiter
climbs high after midnight; it
reaches a peak altitude of 70°
around the time morning twi-
light commences.
A couple of hours after
Jupiter rises, Mars pokes above
the eastern horizon. The Red
Planet moves steadily eastward
against the background stars
during March, crossing from
Ophiuchus the Serpent-bearer
into Sagittarius the Archer in
the month’s second week. Mars
brightens by more than 50 per-
cent during March, climbing
from magnitude 0.8 to 0.3, and
noticeably outshines the stars
of its host constellations.
The rapid brightening goes
hand in hand with the planet’s
increasing diameter. Mars’ disk
spans 6.7" on March 1 and
reaches 8.4" across by the 31st.
This is big enough that youmight catch a f leeting glimpse
of surface detail during
moments of good seeing, when
Earth’s atmosphere steadies
and the light from celestial
objects snaps into sharp focus.
Saturn rises a little more
than an hour after Mars in
early March, but the gap
shrinks to 10 minutes by the
31st. At the end of the month,
they appear 2° apart and make
a fine pair through binoculars.
(The two will pass within 1.3°
of each other April 2.) Saturn
shines at magnitude 0.5 and
appears a touch dimmer than
its neighbor. They’ll be easier
to tell apart by their colors:
Mars shines with a distinctive
orange-red hue while Saturn
appears golden yellow.
It’s always worth exploring
Saturn through a telescope,
though your sharpest views
will come when it climbs high
in the east as dawn starts to
paint the sky. In mid-March,
the planet shows a 16"-diameter
disk surrounded by a ring sys-
tem that spans 37" and tips 26°
to our line of sight. The large
tilt delivers excellent views of
the inky-black Cassini Division
that separates the outer A ring
from the brighter B ring.The starry sky
One of the surprises for many
first-time telescope users is
“discovering” that so many
stars are double or multiple.
The list of such systems is long,
and includes some of the night
sky’s brightest stars.
Probably the first double
that beginners aim their tele-
scopes toward is Alpha (α)
Centauri, which is arguably themost famous double star in the
southern sky. It is also the near-
est star system to our own, with
faint Proxima Centauri, the
system’s third member, the
closest of the three. But it is the
brighter pair that makes a spec-
tacular telescopic sight. Only
4.5" separate the two suns, and
the gap is gradually widening.
Next, turn your attention to
Orion the Hunter. Center your
scope on Rigel, the bright, blue-
white star at the upper left of
the constellation these March
evenings. At medium and high
magnification, the magnitude
6.8 secondary shows up nicely
9" from the primary. Although
the companion is also a double,
the two stars are a fraction of
an arcsecond apart and invis-
ible through backyard scopes.
If you want to see a beauti-
ful multiple star system, look
no further than Sigma (σ)
Orionis. It resides 0.8° south-
southwest of Zeta (ζ) Ori, the
easternmost star in Orion’s
Belt. Small scopes reveal four
stars. In addition to the 4th-
magnitude primary, you’ll see
stars of magnitudes 10.3, 7.5,
and 6.5 in order of their increas-
ing distance. The primary itself
is a very close double, but you
won’t be able to split it.
Our final stop these March
evenings is across Orion’s east-
ern border into Monoceros the
Unicorn. Beta (β) Monocerotis
is a stunning triple star with
components glowing at magni-
tudes 4.7, 5.2, and 6.1. The
second-brightest star resides
7" from the primary, while the
third-brightest member lies
another 3" farther away in
nearly the same direction.