April 2, 5 A.M.
Looking south-southeastSCORPIUSAQUILAOPHIUCHUSSAGITTARIUSMarsAltairSaturnAntares10°Red and ringed planets unite (^)
36 ASTRONOMY • APRIL 2018
Visible to the naked eye
Visible with binoculars
Visible with a telescope
MARTIN RATCLIFFE and ALISTER LING describe the
solar system’s changing landscape as it appears in Earth’s sky.
April 2018: Mars and Saturn rendezvous
SKYTHIS
MONTH
T
he evening sky hosts the
two brightest planets
— Venus and Jupiter —
with the former on view
shortly after sunset and
the latter rising later in the eve-
ning. April mornings belong
to the equally riveting duo of
Mars and Saturn. The Red
Planet grows steadily bigger
and brighter this month as it
approaches a spectacular oppo-
sition in late July. Although
the ringed planet appears a
bit dimmer, it’s always a treat
to view through a telescope.
These two worlds enjoy a
memorable conjunction when
A crescent Moon joins
Venus shortly after midmonth.
If you have clear skies April 17,
be sure to look for the 2-day-
old Moon 5° to the planet’s
left. As the sky darkens, the
Pleiades star cluster (M45)
slowly emerges 9° directly
above Venus. Set against a
deepening twilit sky, the fine
grouping offers a great photo
opportunity. The Moon and
Venus both dip below the hori-
zon around 9:30 p.m. local day-
light time.
The planet moves eastward
relative to the background
stars during April, passing
from Aries into Taurus on the
19th. Venus slides 4° south of
the Pleiades on the 23rd and
ends the month a similar dis-
tance north of the V-shaped
Hyades star cluster. A telescope
reveals little change in the
world’s appearance by April’s
close, however. It then appears
11.5" across and the Sun illu-
minates 89 percent of the disk.
Once Venus slips below the
horizon, it’s not long before
they pass within a couple
of degrees of each other in
early April.
The first object you’ll see
after the Sun sets is Venus.
The dazzling planet shines at
magnitude –3.9 from its perch
low in the western twilight
sky. On April 1, it stands 10°
above the horizon 45 minutes
after sundown. You’ll have
less than an hour to target
Venus through a telescope,
and even then the view leaves
much to be desired. The inner
world shows a bland disk that
appears 10.6" across and
94 percent lit.
Jupiter rises in the east-
southeast. In early April, it’s
up by 11 p.m. local daylight
time; at month’s end, it’s vis-
ible during twilight almost
diametrically opposite Venus.
The giant planet lies in cen-
tral Libra, almost due east of
Zubenelgenubi (Alpha [α]
Librae). The gap between star
and planet closes from 7° to
4° during April.
Jupiter will reach opposi-
tion and peak visibility dur-
ing May’s second week.
Change happens slowly for a
planet this far from the Sun,
however, and its physical
appearance remains nearly
constant during April. Jupiter
brightens almost impercepti-
bly, increasing from magni-
tude –2.4 to –2.5, and a
telescope shows the disk
swelling only from 43" to
45" across.
Your best views of Jupiter
won’t come when it hangs low
in the evening sky, but in the
early morning hours when
Mars and Saturn appeared a few degrees apart against the backdrop it climbs well above the
of Virgo (with blue-white Spica just to their left) in August 2012. The two
planets make a return engagement in Sagittarius in early April. LUIS ARGERICH
Mars and Saturn shine almost equally bright when they pass within 2°
of each other in April’s first few mornings. ALL ILLUSTRATIONS: ASTRONOMY: ROEN KELLY