SOUTHERN
SKY
MARTIN GEORGE describes the solar system’s changing landscape
as it appears in Earth’s southern sky.
July 2018: Red Planet renaissance
July offers planet observers
quite a feast. As twilight deep-
ens in early July, four naked-eye
planets span the sky roughly
from east to west. But it is the
fifth bright planet, which rises
shortly after darkness falls, that
undoubtedly will command the
most attention.
Mars puts on its finest
appearance in 15 years this
month. The ruddy world rises
around 7 p.m. local time July 1.
It then shines at magnitude
–2.2, but it grows noticeably
brighter as it approaches a
splendid opposition on the
27th. Mars gleams at magni-
tude –2.8 during July’s entire
final week. That’s more than
100 times brighter than any of
the stars in its host constella-
tion, Capricornus.
Although the Red Planet
comes to opposition roughly
every 780 days, some of these
close approaches are consider-
ably better than others. This
one is particularly favorable
because the distance to Mars
shrinks to just 57.6 million
kilometers (on July 31), which
is about as close as it can get.
To make this appearance
even better, the planet lies at
a declination of –26°. From
mid-southern latitudes, Mars
passes nearly overhead around
midnight local time and
remains at an altitude above
45° from 9 p.m. to 3 a.m. Its
lofty position means observers
should get sharp views through
their telescopes.
At its closest approach in
late July, Mars’ disk spans 24.3",
and it remains above 20" all
month. Consider using eye-
piece filters to bring out surface
details. Red and orange filters
reveal dark markings well,
while a blue filter shows the
polar regions and clouds more
clearly. Make the most of this
apparition — Mars won’t be as
close again until 2035!
Although Mars rules the
night, don’t overlook July’s
other bright planets. Let’s
tackle them one by one, mov-
ing from west to east across the
early evening sky. First up is
Mercury, which appears low
in the northwest after the Sun
sets. The innermost planet
reaches greatest elongation
July 12, when it lies 26° east
of the Sun and stands 15° high
45 minutes after sundown.
A telescope reveals an
8"-diameter disk that’s slightly
less than half-lit. Over the fol-
lowing 10 days, the planet’s
disk grows while its phase
wanes to a pleasing crescent.
Look to Mercury’s upper
right and you can’t miss Venus.
The brilliant world brightens
from magnitude –4.1 to –4.3 in
July and dominates the evening
sky. Venus spends all month in
Leo the Lion, passing 1.1° north
of 1st-magnitude Regulus on
July 9. When viewed through
a telescope, the planet shows a
disk that grows from 16" to 20"
across during July and a gib-
bous phase that wanes from
70 percent to 57 percent lit.
The solar system’s two larg-
est planets also put on great
shows this month. Jupiter
rides high in the north after
darkness falls. Shining at mag-
nitude –2.2 at midmonth, it
overshadows the background
stars of Libra. Even a small tele-
scope resolves the gas giant’s
equatorial region into two par-
allel dark belts that sandwich
a brighter zone. Larger aper-
tures reveal more atmospheric
details on a disk that measures
40" across.
Last but not least, Saturn
stands as the brightest object
between Jupiter and Mars. The
ringed planet resides in north-
western Sagittarius, just north
of the Archer’s conspicuous
Teapot asterism, and climbs
highest in the north in late eve-
ning. Saturn shines at magni-
tude 0.1 in mid-July, when a
telescope reveals the planet’s
18"-diameter disk surrounded
by a lovely ring system that
spans 41" and tilts 26° to our
line of sight.
A slight partial solar
eclipse occurs July 13 for resi-
dents of southeastern Australia.
From Hobart, Tasmania, the
eclipse lasts from 2h52m
to 3h56m UT, and the Moon
covers 10 percent of the Sun’s
diameter at maximum.
Half a lunar month later, on
July 27, the Moon dips deeply
into Earth’s shadow. People in
Africa and Australia can wit-
ness a total lunar eclipse with
brilliant Mars at opposition just
7° south of the Moon. The
eclipse’s umbral phase begins at
18h24m and ends at 22h19m
UT, while totality runs from
19h30m to 21h13m UT. (In
Australia, the event takes place
before dawn July 28.) The 103
minutes of totality makes this
the longest total lunar eclipse
since 2000.
The starry sky
Southern Hemisphere observ-
ers enjoy a splendid view of the
Milky Way splayed across the
southern sky on July evenings.
Our galaxy’s disk stretches
from the eastern to southwest-
ern horizon, with Crux the
Cross near its center. Although
our eyes tend to focus on the
bright objects, the Aboriginal
people of Australia formed
patterns from the Milky Way’s
dark dust lanes.
Perhaps the best known of
these is the Emu. The most
famous dark nebula in the sky,
the Coal Sack, represents the
Emu’s head. The Coal Sack
tucks up against the southeast-
ern side of the Cross and is easy
to see under a dark sky. It
stands out well with averted
vision, which brightens the
Milky Way and thus increases
contrast, making the Coal Sack
appear darker.
At first sight, the Coal Sack
seems devoid of stars — indeed,
it blocks our view of most
objects beyond. It is far from
empty, however. Pay particular
attention to the open star clus-
ter NGC 4609. It lies 1.8° east of
1st-magnitude Acrux, Crux’s
brightest star, in the direction
of Alpha ( α ) and Beta ( β )
Centauri. The 5th-magnitude
star BZ Crucis dominates this
group, with the remaining stars
spreading out to its northwest.
Based on its estimated dis-
tance of more than 4,000 light-
years, NGC 4609 lies behind the
Coal Sack and shows through
its dust. Although binoculars
show the 7th-magnitude cluster,
it appears most pleasing
through 10-centimeter and
larger telescopes. A magnified
view reveals quite a few stars,
many of them forming pairs.