Astronomy - USA (2020-08)

SKY THIS MONTH

Visible to the naked eye

Visible with binoculars

Visible with a telescope

August 31, 2 A.M.

Looking southeast

10°

TAURUS

Mira

ARIES

PISCES

Mars

CETUS

Diphda

Mars rises high (^)
36 ASTRONOMY • AUGUST 2020
The summertime
planetary bonanza
continues through August as
Jupiter and Saturn maintain
their dominance of the south-
ern sky soon after sunset and
remain visible all night. Jupiter’s
moons offer a triple dose of
combined Io and Ganymede
transits. After midnight, it’s
time for Mars, which is really
brightening now and is a fine
object in telescopes. Together
with the Red Planet, Uranus
and Neptune share a tradition-
ally dim region of the sky. In
the hours before dawn, Venus
provides a treat and Mercury is
visible during the first week of
the month, low in the northeast.
Let’s begin our planetary
sojourn with Jupiter, Saturn,
and the near-Full Moon, which
stand together above the south-
eastern horizon on August 1 in
eastern Sagittarius. The two
giant planets are past opposi-
tion and are 20° high an hour
after sunset in the first week of
the month. By the same time at
the end of the month, they’re
nearing the meridian due south.
The Moon revisits the region
between August 28 and 29.
Jupiter shines at magnitude
–2.7 and dims 0.1 magnitude
during the month. Saturn is
dimmer, at magnitude 0.1 as
August opens and fading to
0.3 during the month. The
planets remain about 8° apart
throughout August.
Jupiter moves westward
relative to the stars in
Sagittarius and arrives less than
6° northeast of Nunki (Sigma
[σ] Sagittarii) by August 31, just
below the teaspoon asterism.
Like a drop of golden syrup
suspended in the sky, Jupiter
dazzles with a yellowish hue
and never disappoints the
telescopic viewer. Its disk spans
47" and shrinks less than 5 per-
cent during the month due to
increasing distance from Earth.
Barring the blurring effects
of our atmosphere, Jupiter
offers a wealth of detail. Its
twin dark equatorial belts jump
out immediately. Once your eye
adjusts to the planet’s brilliance,
more subtle cloud belts and
zones appear. With patience,
you’ll capture f leeting moments
of good seeing.
The Great Red Spot makes
occasional appearances as
it’s carried with the planet’s
9-hour, 55-minute rotation
period. (Jupiter’s equatorial
zones rotate five minutes faster.)
Also popping into view
through any telescope are the
Galilean satellites: Io, Europa,
Ganymede, and Callisto.
Eclipses and occultations of
these four bright moons occur
frequently. Transits of moons
and their trailing shadows are
fascinating to watch, and
sometimes more than one
occurs at the same time. Here
are a few examples to watch for
this month; note that more
occur than are listed here.
Early evening on August 14
finds Jupiter’s largest moon,
Ganymede, transiting the planet.
It exits the disk at 10:51 P. M.^
EDT, visible in darkness in the
eastern half of the U.S. The
moon’s large, dark shadow also
transits this evening, taking
another three hours to do so. In
the meantime, Io is approaching
AUGUST 2020
Outer planets on display
THE SOLAR SYSTEM’S CHANGING LANDSCAPE AS IT APPEARS IN EARTH’S SKY.
BY MARTIN RATCLIFFE AND ALISTER LING
Perseid meteors streak away from
the shower’s radiant in 2018, with the
Milky Way as a backdrop. TONY HALLAS
AL
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The Red Planet is gaining altitude and brightness in the morning sky. Look for
it well above the horizon in the early morning as August progresses.