SOUTHERN
SKY
MARTIN GEORGE describes the solar system’s changing landscape
as it appears in Earth’s southern sky.February 2019: Bright planets at dawn
Only one bright planet manag-
es to grace this month’s early
evening sky. Mars stands out
well, however, because it shines
brightly and occupies a region
of sky devoid of conspicuous
stars. On February 1, the Red
Planet glows at magnitude 0.9
against the backdrop of eastern
Pisces. By month’s end, you can
find the magnitude 1.2 world in
southern Aries.
Mars appears about 20° high
in the northwest as darkness
falls. This relatively low altitude
arises because Southern
Hemisphere observers face a
disadvantage at this time of
year. The ecliptic — the Sun’s
apparent path across our sky
that the planets follow closely
— makes a shallow angle to the
western horizon after sunset.
Thus, Mars’ elongation from
the Sun translates more into
distance along the horizon and
not into altitude above it. From
mid-northern latitudes, Mars
appears twice as high at the
same time.
Unfortunately, the Red
Planet proves disappointing
when viewed through a tele-
scope. Although the dust storm
that enveloped the world at its
peak last year has long since
abated, Mars appears only 6" in
diameter. Its low altitude and
tiny size combine to render
Mars a featureless disk.
Mercury reaches greatest
elongation February 26/27,
when it lies 18° east of the Sun.
But it suffers from the ecliptic’s
low angle as well. The planet
climbs just 3° high a half-hour
after sunset and remains lost in
bright twilight.
No other naked-eye planetappears until after midnight,
but the wait is well worth it.
Jupiter rises first, poking
above the eastern horizon
around 1 a.m. local time in
mid-February. The giant planet
shines at magnitude –2.0, far
brighter than any of the stars
in its host constellation,
Ophiuchus the Serpent-bearer.
Jupiter moves slowly eastward
relative to this starry backdrop
during February.
This gas giant world makes
a wonderful target for telescope
users on any clear morning. Its
large disk — 35" across the
equator and 2" less through
the poles — features plenty of
atmospheric details. And the
planet’s four bright moons typi-
cally change positions notice-
ably in just a few hours.
Although Jupiter is bright, it
pales in comparison to Venus.
You can judge the two easily
February 1, when Venus lies 9°
east of Jupiter and rises less
than an hour after its neighbor.
Venus then shines at magnitude
–4.3, nearly 10 times brighter
than its neighbor. That same
morning, a beautiful crescent
Moon lies just below Venus.
The planet traverses the breadth
of Sagittarius from west to east
during February and leaves
Jupiter far behind. On the 28th,
36° separate the two worlds.
As Venus heads east, it also
moves away from Earth. For
telescope owners, this means
the inner world shrinks while
its phase waxes. On February 1,
Venus shows a disk 19" across
and 62 percent lit. On the 28th,
the planet spans 16" and the
Sun illuminates 72 percent of
its Earth-facing hemisphere.As Venus races across
Sagittarius, it meets up with the
slowest of the bright planets:
Saturn. On the mornings of
February 18 and 19, the two
make an attractive pair despite
magnitude 0.6 Saturn shining
nearly 100 times fainter.
The ringed planet appears
fairly high in the predawn
darkness this month because
the ecliptic angles steeply to the
eastern horizon on February
mornings. Spend some time
viewing magnificent Saturn
through your telescope. You’ll
see a globe measuring 15"
across surrounded by a dra-
matic ring system that spans
35" and tilts 24° to our line
of sight.The starry sky
From the Southern
Hemisphere, many ancient
constellations appear upside
down. Leo the Lion and Taurus
the Bull bear at least some
resemblance to the creatures
they were named after when
viewed right-side up, but that’s
lost when they are reversed.
Probably the most prominent
example is Orion the Hunter.
He stands on his rather small
head, his shoulders hang below
his knees, and his sword seems
to defy gravity. February eve-
nings provide observers with
an excellent view of Orion’s
topsy-turvy world.
When gazing at Orion, peo-
ple often confine their thoughts
to the area enclosed by the four
bright stars marking his knees
and shoulders. But take a few
minutes and look to the west
for the Hunter’s Shield, held up
to defend against the Bull.Most of the bright stars in a
given constellation have Greek
letters associated with them.
Johann Bayer introduced this
system in his Uranometria
atlas, published in 1603. In gen-
eral, Alpha marks a constella-
tion’s brightest star, Beta the
next brightest, and so on.
Many exceptions to this sys-
tem exist, however. One of the
oddest is that, in some cases,
more than one star has the
same Greek letter. In Orion, all
six stars in the shield have the
Greek letter Pi (π)!
How can this be? Well,
Bayer sometimes assigned a
single Greek letter to multiple
stars that appeared close
together, such as Omega^1 (ω^1 )
and Omega^2 (ω^2 ) Scorpii. But in
Orion’s Shield, the Pi designa-
tion covers a string of stars that
spans nearly 10°. Modern star
charts show each star with a
superscript — Pi^1 , Pi^2 , and so
on — running from north to
south. Astronomers added the
numbers after Bayer labeled
them all as Pi.
An even more extreme
example lurks in Orion’s neigh-
boring constellation, Eridanus
the River, which meanders
through much of the southern
sky. In that star group, no fewer
than nine stars go by the name
Tau (τ). They span nearly 20°,
all between –18° and –25° decli-
nation. Take a look at magni-
tude 3.7 Tau^4 , the brightest in
this collection. It is one of the
reddest naked-eye stars in our
night sky, and is the most
strongly colored of Eridanus’
Tau stars. It makes a fine exam-
ple of the admittedly subtle
variations in star colors.