— Continued from page 37
WHEN TO VIEW THE PLANETS
EVENING SKY MIDNIGHT
Venus (west)
Jupiter (southeast) Jupiter (south)
Saturn (southeast)
transit Jupiter’s disk along with
their shadows. Earlier this year,
each moon’s shadow crossed
before the moon itself. But
around the time of opposition,
when the Sun lies behind Earth
as we look toward Jupiter, the
moons and shadows practically
overlap. On May 7, for exam-
ple, Io’s shadow touches the
jovian cloud tops at 10:56 p.m.
EDT — just two minutes
before Io itself. The moon and
shadow both leave Jupiter’s
disk at 1:06 a.m. Contrast this
with the scene May 30, when
Io transits starting at 10:37 p.m.
but the shadow doesn’t hit the
planet until 30 minutes later.
While Jupiter deserves
plenty of attention, the parade
of viewing treats continues
42
A ST R O N O M Y • MAY 2018
S
Callisto
MORNING SKY
Mercury (east)
Mars (south)
Jupiter (southwest)
Saturn (south)
Uranus (east)
Neptune (southeast)
until dawn. Next up is
Saturn, which rises shortly
after midnight local daylight
time in early May and some
two hours earlier by month’s
end. For the best views, how-
ever, wait until it climbs
higher in the south an hour
or two before twilight starts
to paint the sky.
The ringed planet resides
among the background stars
of Sagittarius, just north of
that constellation’s Teapot
asterism. On May 1, it stands
nearly 4° northeast of 3rd-
magnitude Lambda (λ)
Sagittarii, the star marking the
top of the Teapot’s lid, and 1.7°
north of the 5th-magnitude
globular star cluster M22.
Saturn moves slowly westward
COMETSEARCH
PANSTARRS makes its closest approach
The distant Oort Cloud continues
to send cometary messengers
into the inner solar system. Its
best current envoy — Comet
PANSTARRS (C/2016 R2) —
should glow at 10th or 11th mag-
nitude this month. But the comet
exceeded astronomers’ expecta-
tions earlier this year, so there’s
hope it could glow brighter.
PANSTARRS reaches perihe-
lion, its closest approach to the
Sun, on May 9. Even then, how-
ever, it lies in the midst of the
asteroid belt some 2.6 times far-
ther from the Sun than Earth is.
At that distance, our star can’t
warm the comet’s nucleus
enough to make it glow brightly.
But the great distance also means
Track down Jupiter’s satellites
C/2016 R2 moves slowly against
the background stars, and it will
remain a tempting target in the
northwest after darkness falls.
Several nearby bright stars
should make it relatively easy
to track down the comet. In
early May, PANSTARRS lies just
2° south of magnitude 0.1
Capella. And shortly after mid-
month, the comet passes a simi-
lar distance north of magnitude
1.9 Beta ( β ) Aurigae.
A 4-inch telescope under a
dark sky should be enough to
capture the comet’s fuzzy glow,
but an 8-inch scope will allow
you to pick out some structure.
You’ll want to use a fairly high
power to get the best views.
W
Europa
Io
Jupiter
Ganymede
2'
May 8, 11:30 P.M. EDT
The gas giant’s moons are easy to see through a telescope, but identifying
them can be tricky. Their arrangement at opposition makes the task easy.
during May, ending the month
1.8° northwest of M22.
Saturn brightens from mag-
nitude 0.3 to 0.2 during May. It
far outshines Sagittarius’ stars,
and its yellow glow makes it
easy to identify. The planet
will brighten a bit more, to
magnitude 0.0, by opposition
in late June.
Like Jupiter, Saturn’s
appearance through a tele-
scope doesn’t change much in
May. But that’s a good thing,
because few celestial objects
rival the beautiful ringed
world. In mid-May, the planet’s
disk measures 18" across while
the rings span 40" and tilt 26°
to our line of sight. Even small
scopes reveal the Cassini
Division, a dark gap that sep-
arates the outer A ring from
the brighter B ring. Small
instruments also show
Saturn’s brightest moon,
8th-magnitude Titan.
Although you won’t notice
much change with Jupiter and
Saturn this month, Mars
improves dramatically. The
Red Planet is just two months
away from a late July opposi-
tion that will bring it closer to
Earth than it has been in 15
years. Observers will notice a
rapid buildup toward this
peak in May — Mars doubles
in brightness (from magni-
tude –0.4 to –1.2), and its
angular diameter grows by
a third (from 11" to 15").
Comet PANSTARRS (C/2016 R2)
N
s
k
31
26
21
16
/
11
E
Capella
6
`
May 1
Path of
Comet PANSTARRS
AURIGA
l
1°
Brilliant Capella and 2nd-magnitude Beta (β) Aurigae make convenient
guideposts for tracking down this modest comet on May evenings.