Astronomy - 06.2019

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Path of Comet ASASSN

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June 15

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CETUS

0.5°

Comet ASASSN (C/2018 N2)

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Ganymede

Europa

Io

Callisto Jupiter

June 11, 4:00 A.M. EDT 1'

Hunt down Jupiter’s four bright satellites

42 ASTRONOMY • JUNE 2019

COMETSEARCH

Comet observers often hope a

new discovery will herald a

bright target to feed their pas-

sion. This does happen, though

not often. Two arrivals bright-

ened to 9th magnitude in late

2018, but unless we get a similar

surprise this month, we’ll have to

be satisfied with a comet that

reaches only 12th magnitude.

To catch Comet ASASSN

(C/2018 N2), wait for the Moon-

free period at the end of June.

ASASSN — short for the All-

Sky Automated Survey for

Supernovae program — then

resides in northeastern Cetus

the Whale and rises about an

hour before morning twilight

commences. Look for the faint

smudge of light as it glides

northward between magnitude

4.9 Nu (ν) Ceti and magnitude

4.3 Xi^2 (ξ^2 ) Cet. Astronomers dis-

covered this comet in July 2018,

and it appears destined to peak

at 11th magnitude this autumn.

A harder target lies on the

border of Centaurus and Lupus

in early June. Comet ATLAS

(C/2017 M4) passes between

magnitude 2.7 Beta (β) Lupi and

magnitude 3.1 Kappa (κ) Centauri

during June’s first week. You’ll

need a 12-inch or larger scope to

spot this 13th-magnitude object.

A killer takes aim at the Whale

EVENING SKY MIDNIGHT MORNING SKY

Mercury (northwest) Jupiter (south) Venus (northeast)
Mars (northwest) Saturn (southeast) Jupiter (southwest)

Jupiter (southeast) Saturn (southwest)
Uranus (east)
Neptune (southeast)

WHEN TO VIEW THE PLANETS

— Continued from page 37

Red Spot appears about half
the time — whenever the plan-
et’s 10-hour rotation carries it
onto Jupiter’s Earth-facing
hemisphere.
The sharpest views of the
giant world come when it lies
highest in the south. Jupiter
peaks at an altitude of about
30° at 1 a.m. local daylight
time the night of opposition. It
reaches the same benchmark
about a half-hour earlier with
each passing week. Still, the
planet lies nearly as high and
the views are almost as good
for a couple of hours on either
side of these times.
Jupiter’s four brightest
moons create a scene that
changes dramatically from
night to night. Their motions
sometimes appear noticeable
even within minutes, particu-
larly when a satellite transits

minutes, you should notice its

shadow immediately to the

moon’s east, with the two over-

lapping. Ganymede lies north

of Io and begins to transit at

11:28 p.m. Its shadow falls on

the cloud tops just southeast of

the moon. Because Ganymede

lies farther from Jupiter than

Io, its shadow appears slightly

more separated from the

moon. Io completes its transit

at 12:33 a.m., when Ganymede

is about halfway across the

giant planet’s disk. The outer

moon completes its trek

around 1:40 a.m.

Saturn lies 30° east of

Jupiter, which means it trails

about two hours behind its

bigger brother. The ringed

planet rises around 11 p.m.

local daylight time June 1 and

some two hours earlier by

month’s end.

the planet’s face or lies near

the limb.

The night of opposition

offers a good opportunity to

acquaint yourself with these

so-called Galilean moons. If

you look during the morning

hours of June 11, you’ll see Io,

Europa, and Ganymede lined

up to Jupiter’s east while

Callisto stands alone to the

planet’s west.

The month’s most dra-

matic scene occurs the follow-

ing night, however. Both Io

and Ganymede start to cross

Jupiter’s disk the evening of

June 11. But with the gas giant

so close to opposition, the

shadow that each satellite

casts falls onto the jovian

cloud tops almost directly

beneath the moon.

Io’s transit begins at

10:22 p.m. EDT. Within five

Saturn lies in northern

Sagittarius, just south of that

constellation’s Teaspoon

asterism. It shines at magni-

tude 0.2 in mid-June and

appears four times brighter

than any of the Archer’s stars.

The best time to view

Saturn through a telescope

occurs during the early morn-

ing hours when it climbs

highest in the south. Even the

smallest telescope delivers

stunning views. The planet’s

disk measures 18" across

while the rings span 41" and

tilt 24° to our line of sight.

Saturn’s disk shows little

detail, though you might spot

an equatorial belt and a dark

polar hood.

Although Saturn’s moons

don’t glow as brightly as

Jupiter’s Galilean satellites,

small scopes reveal at least

Reserve some time on June mornings to track down this faint comet as it

slides to the northeast against the background stars of Cetus.

The giant world’s moons show up nicely through small scopes, but they can

be tricky to identify. Their arrangement at opposition makes the task easy.