Sky and Telescope - April 2017 - 46

APRIL 2017 OBSERVING
Sun, Moon & Planets by Fred Schaaf

Mercury Maxes Out
The tiny planet climbs to its highest altitude of the year in April, while Jupiter reaches opposition.

ightfall brings majestic Jupiter
into view low in the east, while
far dimmer Mars descends in the west.
Well below Mars, Mercury remains
visible for about the ﬁrst ten days of
April, after which it fades into the solar
glare. Saturn rises in the middle of the
night, around the time Jupiter shines at
its highest. Then, in early dawn, Saturn
reaches its apex in the south while blazing Venus bursts above the east horizon.

E A R LY E V E N I N G
On April 1st, Mercury appears at its
highest altitude of the year at nightfall
for viewers around latitude 40° north.
It's also at greatest eastern elongation,
19° from the Sun, and its magnitude
-0.2 light doesn't set until more than
1½ hours after the Sun.
But this ﬁne presentation doesn't last
for long. By the evening of April 8th,

Mercury's phase in telescopes decreases
from 43% to 16% lit and its brightness
fades by more than 1½ magnitudes.
Mercury stands about 7° above the
west-northwest horizon 45 minutes
after sunset that day, with Mars 17° to
its upper left. A few days later, the little
planet is too dim to detect in the bright
twilight sky. Mercury passes through
inferior conjunction on April 20th
before reappearing at dawn at the very
end of the month.
Mars stands about 20° high in the
west one hour after sunset in early
April, but only about 10°-12° high at
a comparable time at the end of the
month. Mars dims just a bit during April, dropping from magnitude
+1.5 to +1.6. Already quite small in
the eyepiece, its disk shrinks just a bit
more, down to less than 4″ in apparent
diameter.

Mars does, however, make a pretty
passage between the Pleiades and Hyades in the last week of the month. The
Red Planet shines 10° directly below
the Pleiades on April 7th. During the
next two weeks it creeps upward and
to the left of the star cluster, closing
the gap between to about 3° on April
20-22. Mars ends April upper left of the
Pleiades, right of the Hyades, and about
7° right of Aldebaran, which is similarly
colored and distinctly brighter.

D U S K TO DAW N
Jupiter comes to opposition on April
7th and so is visible all night at its closest, brightest, and biggest of the year;
see page 48. This opposition, however,
occurs less than two months after
Jupiter reaches aphelion (the gas giant's
farthest point from the Sun in space) of
its 12-year orbit. For only a few weeks

Dusk, April 6

Dusk, April 9 -11

Dawn, April 15 -16

1 hour after sunset

1 hour before sunrise

Moon
Apr 5

LEO

Moon
Apr 16

Moon
Apr 9

Saturn

aVir

Moon
Apr 6
Regulus

Moon
Apr 10

Moon
Apr 15

Jupiter

Antares

SCORPIUS

Moon
Apr 7
Spica

Moon
Apr 8

Looking Southeast, up high

A P R I L 2 0 1 7 * SK Y & TELESCOPE

Moon
Apr 11

Looking East-Southeast

Looking South

Sky and Telescope - April 2017

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