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SOUTHERN SKY BY MARTIN GEORGE
August 2020
Venus gleams before dawn
Despite the cool win-
ter nights, August
promises to be a great month
for viewing the solar system’s
two largest planets. Jupiter and
Saturn form a beautiful pair in
the eastern sky as darkness
falls and pass nearly overhead
later in the evening.
Brilliant Jupiter dominates
the scene. The giant planet
shines at magnitude –2.7 dur-
ing the first half of August, just
0.1 magnitude shy of its peak at
opposition in July. You can find
Jupiter set against the back-
ground stars of eastern
Sagittarius, though the planet
makes a better guide to the
constellation than vice versa.
When viewed through a
telescope, the massive world
spans 46" and shows a wealth
of atmospheric detail. You’ll
immediately notice two dark
bands that sandwich a brighter
zone coinciding with Jupiter’s
equator. During moments of
steady seeing, more subtle fea-
tures snap into view. Also
watch for the dark shadows of
Jupiter’s four big moons when
they transit the planet’s disk.
You can find Saturn less
than 10° below Jupiter on
August evenings. The ringed
planet shines at magnitude 0.2,
nearly 15 times fainter than its
companion but still much
brighter than any nearby star.
Like Jupiter, Saturn resides in
eastern Sagittarius, but it is
much closer to the border with
neighboring Capricornus.
Saturn never fails to impress
first-time telescope users, and it
even ranks as a favorite among
more seasoned veterans. In
mid-August, the planet’s disk
measures 18" across while the
rings span 42" and tilt 22° to
our line of sight. The dark
Cassini Division that separates
the outer A ring from the
brighter B ring shows up nicely
in good seeing conditions.
The ruddy glow of Mars
pokes above the eastern hori-
zon later in the evening. The
Red Planet nearly doubles in
brightness during August,
climbing from magnitude –1.1
to –1.8. It far outshines the
background stars of its host
constellation, Pisces the Fish.
Mars grows brighter because
it continues to pull closer to
Earth in advance of its mid-
October opposition. This also
makes the nearby planet a wor-
thy target for telescope users.
Mars’ angular diameter swells
from 15" to 19", which is big
enough to reveal several dusky
surface markings. The planet’s
south polar cap also stands out
because it now tilts noticeably
in our direction.
A waning gibbous Moon
occults Mars across southern
and southeastern South
America on August 9. From
Buenos Aires, Mars disappears
behind the Moon’s bright limb
at 7h44m UT and reappears
from behind the dark limb at
8h58m UT — though be sure
to start watching a few minutes
before these times to see the
whole event. The planet’s disk
takes a minute or so to com-
pletely disappear and reappear.
Shortly before morning twi-
light starts to paint the sky,
Venus emerges in the east-
northeast. You won’t mistake
the planet for any other celestial
object. Gleaming at magnitude
–4.4 in mid-August, Venus
shines five times brighter than
Jupiter. The inner world begins
the month 2° south-southwest
of 3rd-magnitude Zeta (ζ) Tau r i,
the southern horn of Taurus the
Bull. It crosses into northern
Orion on August 5 and remains
within the Hunter’s boundaries
when it reaches greatest elonga-
tion on the 13th. Venus then lies
46° west of the Sun and stands
20° above the northeastern
horizon an hour before sunrise.
The planet enters Gemini later
that same day and remains
among the Twins’ stars the rest
of the month.
When viewed through a
telescope this month, Venus
shows a large disk that never-
theless shrinks noticeably (from
27" to 20" across) as it waxes
from a crescent to gibbous
phase. It should appear half-lit
the morning of its greatest
elongation.
You might catch a glimpse
of Mercury on August’s first
morning. The innermost planet
then shines at magnitude –0.9
and lies 5° high in the north-
east a half-hour before sunup. It
vanishes into twilight in the
next day or two.
The starry sky
The Orion Nebula (M42) has
to rank at the most frequently
observed nebula in the sky. Its
size, brightness, and location
near the celestial equator
(which makes it a beautiful
object for observers on both
sides of the equator) make it
nearly irresistible.
At this time of year, how-
ever, when the Milky Way
rides high in the Southern
Hemisphere’s evening sky, two
other nebulae give M42 a run
for its money. The Lagoon
Nebula (M8) and Trifid Nebula
(M20) both reside in western
Sagittarius. The 18th-century
French astronomer Charles
Messier included both objects
in his famous catalog.
The Lagoon, in particular,
is a treat to view. You can find
it 5° west and a bit north of
magnitude 2.8 Lambda (λ)
Sagittarii. Visible with the
naked eye on a dark night away
from city lights, M8 is easy to
see through binoculars. A small
telescope at low magnification
shows a wonderful field that
includes the dark dust lane near
the nebula’s center that gives
the Lagoon its name. M8’s
brightest star is 6th-magnitude
9 Sagittarii, which glows with a
distinct blue-white color.
The fainter Trifid Nebula
lies 1.4° north of the Lagoon. A
20-centimeter or larger tele-
scope at medium magnification
gives a nice view of the three
dark lanes from which the neb-
ula takes its name. M20 pro-
vides a great example of how
averted vision can enhance
your view — if you look to the
edge of the field, the Trifid’s
dust lanes pop into view.
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