SOUTHERN SKY BY MARTIN GEORGE
October 2020
The Red Planet returns to glory
As darkness falls in
early October, a glitter-
ing array of planets spreads
across the sky. You’ll want to
make Mercury your first tar-
get. For Southern Hemisphere
observers, the innermost planet
puts on its best evening show of
the year during spring. To
locate the diminutive world,
first find majestic Scorpius
halfway up the western sky
about an hour after sunset.
Mercury is the brightest object
below the Scorpion.
The planet reaches greatest
elongation October 1. It then
lies 26° east of the Sun and
stands 12° high an hour after
the Sun goes down. Glowing at
magnitude 0.0, Mercury out-
shines every other object in the
vicinity. Although the planet
dims slowly during the next two
weeks, its appearance through a
telescope improves. On the 1st,
Mercury appears 6.7" across
and 61 percent lit. A week later,
the world spans 7.6" and the
Sun illuminates just under half
of its disk. The planet grows
larger and displays a thinning
crescent until it disappears in
twilight around midmonth.
Once you’ve spent some
time with Mercury, shift your
gaze to the opposite side of the
sky for magnificent Mars. The
Red Planet reaches opposition
and peak visibility October 13,
when it rises at sunset and
climbs highest in the north
around midnight local time.
The ruddy world shines bril-
liantly at magnitude –2.6 and
appears as a warm beaconamong the dim stars of Pisces.
Mars moves slowly westward
relative to the Fish’s stars this
month as Earth overtakes it on
our planet’s faster, smaller orbit
around the Sun.
This is the best time to
observe Mars through a tele-
scope in more than two years.
The planet spans 22.6" at its
closest during October’s first
week, but it remains above 20"
all month. Watch for subtle
dark markings on the other-
wise ocher surface, and be sure
to notice the bright white south
polar cap. The south polar
region stands out because it
tilts about 20° toward us.
After viewing the solar sys-
tem’s two smallest planets, turn
your attention to the two larg-
est. Jupiter and Saturn pass
nearly overhead shortly after
sunset. The two appear just a
few degrees apart against the
backdrop of Sagittarius, north-
east of the Archer’s distinctive
Te a p o t a s t e r i s m.
Jupiter shines at magnitude
–2.3 in mid-October, just a
shade dimmer than Mars. And
with an equatorial diameter of
39", it remains a splendid tele-
scopic sight. During moments
of good seeing, the gas giant’s
atmosphere resolves into an
alternating series of bright
zones and darker belts punctu-
ated with smaller sites of turbu-
lence near their borders. Also
keep an eye out for Jupiter’s
four brightest moons, which
show up through any scope.
Magnitude 0.5 Saturn pales
in comparison with Jupiter butfar outshines the background
stars of Sagittarius. The ringed
planet lies east of its planetary
companion, though the gap
between the two worlds shrinks
from 7° to 5° this month. Any
telescope reveals Saturn’s
17"-diameter disk surrounded
by a splendid ring system that
spans 38" and tilts 23° to our
line of sight. You should also
see the planet’s brightest satel-
lite, 8th-magnitude Titan.
Venus doesn’t clear the
horizon until a few minutes
before morning twilight starts
to paint the sky. The brightest
planet remains conspicuous,
however, because it shines bril-
liantly at magnitude –4.0. You
can find it low in the east as
twilight brightens. The inner
planet has lost much of its tele-
scopic appeal from earlier this
year. In mid-October, Venus
spans 14" and appears about
three-quarters lit.The starry sky
A quick look at any good star
atlas will show labels attached
to many stars. Some have prop-
er names, such as Sirius and
Canopus, but these and others
are also often marked with
the Greek letters 17th-century
German astronomer Johann
Bayer assigned to them. And
in many cases, a number also
appears next to a star.
The numbers, which reach
as high as 140 (in the constella-
tion Taurus the Bull), owe their
existence to a star catalog pro-
duced by England’s first
Astronomer Royal, JohnFlamsteed (1646–1719). Yet
Flamsteed himself did not
assign these numbers.
Following a complex history
that involved Isaac Newton,
Edmond Halley, and Johann
Bode, the numbers we use
today are the ones that
appeared in 18th-century
French astronomer Jérôme
Lalande’s 1783 almanac.
However, astronomers then
and now still refer to them
as Flamsteed numbers.
As important as the original
catalog was, it contained many
errors. It included nonexistent
stars and even Uranus, which
was cataloged as 34 Tauri.
From his observatory in
Greenwich, England, Flamsteed
could see no farther south than
a declination of about –38°. So
his catalog did extend into the
southern half of the celestial
sphere, but only so far.
The southernmost star with
a Flamsteed number is Upsilon
(υ) Scorpii, which appears as
34 Sco in the catalog. Almost as
far south is Shaula (Lambda [λ]
Scorpii), which is number 35.
Together, the two form the
Scorpion’s Stinger, which you
can find halfway up in the
west-southwest during
October’s early evening hours.
While gazing in this direction
and thinking of the famous
Astronomer Royal, grab your
binoculars and scan the lovely
star fields in this part of
Scorpius. You can find two
of my favorite open star clus-
ters, M6 and M7, just 5° from
Shaula.