Astronomy

1°

E

AURIGA

Capella

Path of

Comet PANSTARRS

May 1

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31

26

21

16

11

6

s

k

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l

Comet PANSTARRS (C/2016 R2)

May 8, 11:30 P.M. EDT 2'

W

S

Ganymede

Io Europa

Callisto

Jupiter

Track down Jupiter’s satellites

42 ASTRONOMY • MAY 2018

COMETSEARCH

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

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.

PANSTARRS makes its closest approach

EVENING SKY MIDNIGHT MORNING SKY
Venus (west) Jupiter (south) Mercury (east)
Jupiter (southeast) Saturn (southeast) Mars (south)
Jupiter (southwest)
Saturn (south)
Uranus (east)
Neptune (southeast)

WHEN TO VIEW THE PLANETS

— Continued from page 37

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

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

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

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").

Brilliant Capella and 2nd-magnitude Beta (β) Aurigae make convenient

guideposts for tracking down this modest comet on May evenings.

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.