SOUTHERN
SKY
MARTIN GEORGE describes the solar system’s changing landscape
as it appears in Earth’s southern sky.June 2019: Jupiter reigns all night
Giant Jupiter no doubt will gar-
ner the lion’s share of attention
in June, but skywatchers won’t
want to miss seeing the solar
system’s two smallest planets
meet low in the northwest
after sunset.
Early in the month, Mars
stands alone in the deepening
twilight. Although the Red
Planet has been visible in the
evening sky for nearly a year,
it has faded considerably fol-
lowing its spectacular opposi-
tion in July 2018. Shining at
magnitude 1.8, the ruddy world
appears as a modestly bright
object among the background
stars of Gemini. You can find it
to the left of the Twins’ bright-
est stars, Castor and Pollux.
Unfortunately, Mars’ disk spans
only 4" and shows no detail
through a telescope.
As the month progresses,
Mercury joins Mars in the eve-
ning twilight. The inner planet
appears during June’s second
week and climbs higher with
each passing day. Binoculars
deliver the best views as the
two worlds approach each other
over the next 10 days. On the
evening of June 18, Mercury
slides just 0.2° north of Mars.
Although Mercury is
smaller than its outer cousin, it
appears much brighter (magni-
tude 0.1) because it lies consid-
erably closer to Earth. The
innermost planet reaches its
greatest elongation from the
Sun on June 23, when it lies 25°
east of our star and appears
nearly 10° above the northwest-
ern horizon an hour after sun-
set. The view of Mercury
through a telescope improves
as it draws closer to the Sunafter greatest elongation. By
the end of June, the Sun illumi-
nates barely one-quarter of the
world’s 9"-diameter disk.
Despite the appeal of Mars
and Mercury, the solar system’s
showpiece object in June has to
be Jupiter. The giant planet
reaches opposition and peak
visibility June 10, though it
remains essentially unchanged
all month. Shining at magni-
tude –2.6, it stands out beauti-
fully in the eastern evening sky.
Jupiter currently resides against
the backdrop of Ophiuchus
the Serpent-bearer, below the
long string of stars that forms
Scorpius the Scorpion.
The planet quickly ascends
during the course of the eve-
ning and passes nearly over-
head around midnight local
time. Its high altitude delivers
superb views through even the
smallest telescopes. Jupiter’s
disk spans 46" across the equa-
tor and 43" through the poles,
a difference that’s easy to see
once you know to look for it.
And note the two dark cloud
belts sandwiching a brighter
zone that coincides with the gas
giant’s equator. Jupiter’s four
bright moons — Io, Europa,
Ganymede, and Callisto — also
appear prominent as long as
they are not passing in front of
or behind the jovian disk.
Saturn is the next planet to
rise. Its path across the night
sky follows Jupiter’s, but it trails
its sibling by a little more than
two hours. The ringed planet
appears as an interloper among
the stars of Sagittarius, though
at magnitude 0.2, it shines
noticeably brighter than any
of the Archer’s stars.The best time to view
Saturn through a telescope
comes when it climbs highest
in the north after midnight.
Any instrument reveals a
golden-colored globe that mea-
sures 18" across surrounded by
a gorgeous ring system that
spans 41" and tilts 24° to our
line of sight. Also keep an eye
out for Saturn’s satellites. The
brightest, 8th-magnitude Titan,
shows up through any scope.
A nearly Full Moon occults
Saturn on the night of June
18/19 for observers in the south-
ern third of South America and
southern Africa. From Santiago,
Chile, the planet disappears
behind the bright limb at
2h04m UT and reappears at the
dark limb at 3h00m UT.
The brightest planet makes
a brief appearance in morning
twilight during June. Venus
shines at magnitude –3.8, three
times brighter than its closest
competitor, Jupiter. But the
inner planet rises in the east-
northeast only 90 minutes
before the Sun in early June
and less than an hour before
our star at month’s close. A
telescope shows the planet’s
10"-diameter disk and nearly
full phase.The starry sky
The Milky Way appears glori-
ous this time of year, stretching
high across the southern sky in
midevening. Embedded within
this band of light are a promi-
nent constellation, Crux the
Cross, and the Pointers —
Alpha (α) and Beta (β)
Centauri — just to its east.
Alpha Cen is likely the
most famous double star forSouthern Hemisphere observ-
ers. So, it seems to be an odd
quirk of history that its duplic-
ity was discovered from India
in the Northern Hemisphere.
The honor goes to Father
Jean Richaud, whose interest in
astronomy began in France.
Along with thirteen other
Jesuits picked by Louis XIV,
he left France for Siam (as
Thailand was then known) in
1687, where he continued his
astronomical observations.
After a palace revolution in
1688, Richaud left Siam for
India, arriving in Pondicherry
(now Puducherr y) in early- While observing the
Great Comet of 1689 in the
early morning hours, he
trained his telescope on
Alpha Cen and noticed its
fainter companion.
It shouldn’t surprise you
to learn that Puducherry lies
only a bit north of the equator.
From its latitude of 12° north,
the Southern Cross and the
Pointers climb well clear of the
southern horizon when the
time of year and time of night
are right.
The separation of Alpha
Cen’s two components was 7"
in 1689, much less than the
maximum possible of 21.8",
which occurred most recently
in 1980. If you observe Alpha
Cen through a small telescope
at low power now, however, you
might not notice that it is a
splendid double. That’s because
the two stars’ current separa-
tion is only 5.2". Through larger
scopes or higher magnifica-
tions, you should resolve the
yellow primary and orange
secondary.