Sky and Telescope - April 2018 - 47

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almanac.

December
solstice

shining all night at its brightest and
biggest, on May 8-9.

Uranus

M I D N I G H T TO DAW N
Mars and Saturn are a glorious couple
in the opening days of April when they
rise close together around 2:15 a.m.,
and are highest just after sunrise. They
are a minimum of 1.3° apart at dawn
of April 2nd, but essentially are as close
together on the mornings before and
after. On the day of minimum separation Mars is magnitude +0.3 and Saturn
+0.5, orange-gold and rich gold in hue,
respectively. Their equatorial diameters
are about 8½″ for Mars and 17″ for
Saturn, with the superbly tilted rings
spanning about 2½ times the size of
Saturn's globe.
Mars and Saturn have their encounter just a few degrees to the upper left of

Dusk, April 23-24
1 hour after sunset

a
Moon
Apr 23

LEO
Moon
Apr 24

Regulus

Looking South, high in the sky

Dusk, April 27
45 minutes after sunset
Aldebaran
Venus

Sept.
equinox

March
equinox

Jupiter

Sun
Saturn

Neptune

Earth

Mercury

Mars

June
solstice

ORBITS OF THE PLANETS
The curved arrows show each planet's movement during April. The outer planets don't change
position enough in a month to notice at this scale.

Lambda (λ) Sagittarii (Kaus Borealis),
the top star of the Teapot of Sagittarius.
But Mars races on eastward away from
Saturn during April, increasing the gap
between them to 2° on April 5th, a
little more than 5° on April 12th, and
more than 14° on April 30th. During
April, Saturn brightens from magnitude +0.5 to +0.3, but Mars kindles
from +0.3 to -0.4, veritably doubling
in brightness. The apparent width of
Mars swells from 8½″ to 11″ during
April, bringing some surface features
into range of medium-size telescopes on
nights of excellent "seeing."
By the way, dauntingly dim Pluto,
magnitude +14, is 1.4° north of Mars
on the morning of April 26th.
By the end of April, Mars still rises
well after midnight, in fact not long
after 1:30 a.m. By month's end, Saturn
appears above the east-southeast horizon at roughly 12:15 a.m.
Something awesome to note is that
on the North American night of April
16-17 Saturn, at almost the same time
it begins retrograde (westward) motion,
reaches aphelion (farthest from the Sun

Pleiades

Looking West-Northwest

Venus

t These scenes are drawn for near the middle
of North America (latitude 40° north, longitude
90° west); European observers should move
each Moon symbol a quarter of the way toward
the one for the previous date. In the Far East,
move the Moon halfway. The blue 10° scale bar
is about the width of your fist at arm's length.
For clarity, the Moon is shown three times its
actual apparent size.

in space) for the ﬁrst time in 30 years.
Saturn then lies 10.07 a.u. from the Sun
(only a tad closer than in 1959). That is
slightly more than 1 a.u. farther than
Saturn will be at its next perihelion
(closest to Sun in space) in 2032.

DAW N
Mercury spends the month going from
inferior conjunction with the Sun on
April 1st to a greatest western elongation of 27° on April 29th. But this is the
lowest morning apparition of Mercury
in 2018 for viewers at mid-northern
latitudes. Even when highest at month's
end, Mercury is less than 10° above the
horizon even at sunrise.

M O O N PAS SAGE S
The Moon is fat waning gibbous when
it is around 5° upper right of Jupiter on
the morning of April 3rd. The Moon is
nearing last quarter when it's less than
2° upper right of Saturn (itself less
than 3° upper right of Mars) at dawn
on April 7th. The slender waxing lunar
crescent is almost 6° left of Venus at
nightfall on April 17th and within the
Hyades 24 hours later. The waxing gibbous Moon is some 3° left of Regulus
at nightfall on April 24th. The Moon is
full on the North American evening of
April 29th and joins Jupiter in Libra.
¢ FRED SCHAAF had his first view of
a very blue Uranus in a telescope as a
teenager over half a Uranus orbit ago.
sk yandtelescope.com * A PR I L 2 018

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Sky and Telescope - April 2018

Table of Contents for the Digital Edition of Sky and Telescope - April 2018