Astronomy - USA (2019-10)

WHEN TO

VIEW THE

PLANETS

October 1, 11:30 P.M. EDT 2'

Saturn

Rhea Te t h y s

Dione

Iapetus Titan

S

W

E

AQUARIUS

PISCES

b

Path of Comet Africano

Oct 1

3

5

7

9

g

d

c

a

g

h

q

o

N

2°

Iapetus glows at its brightest

COMET SEARCH I Swimming with the Fish

COMET AFRICANO (C/2018 W2)

peaked around 9th magnitude

when it came closest to Earth

on September 27, and it should

maintain this brightness into early

October. Although not a good

target for suburban observers, it

is ripe for viewing from dark-sky

sites through a 4-inch telescope.

Once you home in on the comet,

crank up the power as much as the

night and your scope will allow

to get a close-up view. In early

October, its fan-shaped dust tail tilts

nearly edge-on, so it looks like a

narrow slice of pizza instead of a

formless round blob. Its southern

edge should appear concentrated

and contain a nearly pointlike false

nucleus. Imagers likely can capture

a greenish or bluish glow on the

comet’s eastern flank where

sunlight ionizes escaping gas.

Astronomers Brian Africano

and Hannes Groeller first spotted

this comet within minutes of

each other November 27, 2018. During October’s first week, it passes from Pisces the Fish into Aquarius

the Water-bearer. This region lies due south and about halfway to the zenith in late evening. You can find

Africano 2° southwest of 5th-magnitude Kappa (κ) Piscium the evening of October 1 and the same

distance northwest of 3rd-magnitude Delta (δ) Aquarii on the 7th.

Comet Africano (C/2018 W2)

south as darkness falls in early

October and nearly as high in

the south-southwest as the

month closes.

The ringed planet shines

at magnitude 0.5, besting the

Archer’s brightest star by a fac-

tor of three. Saturn’s yellow

glow stands out nicely between

the constellation’s Teapot and

Teaspoon asterisms, just east of

the Milky Way’s star-studded

bulge. The scene looks magnifi-

cent with the naked eye or bin-

oculars from under a dark sky.

But make sure to target

Saturn through a telescope.

Any instrument shows the

planet’s 16"-diameter disk sur-

rounded by a majestic ring sys-

tem that spans 37" and tips 25°

to our line of sight. The large

tilt provides an exquisite look

at the rings’ structure, reveal-

ing the dark Cassini Division

that separates the outer A ring

from the brighter B ring.

Speaking of viewing angles,

Saturn reaches quadrature

October 7. If you were to draw a

line from the Sun to Earth and

then to Saturn, it would form a

90° angle. To an observer,

quadrature means the shadow

cast by Saturn falls as far east of

the planet as possible and hides

a noticeable section of the rings’

farside. The effect gives the

planet a distinct 3D look that

lasts for several weeks.

Saturn boasts several

moons within reach of ama-

teur telescopes. The brightest

is 8th-magnitude Titan, which

shows up through any scope.

You can find it north of Saturn

on October 1 and 17 and south

of the planet on the 9th and

25th.

A 4-inch instrument pulls

in four more satellites. Tethys,

Dione, and Rhea are the easiest

to find. All three lie closer to

Saturn than Titan and circle

the planet in less than a week.

Iapetus proves a bit trickier.

This outer moon glows at 10th

magnitude when its bright

hemisphere faces Earth at great-

est western elongation the night

of October 1/2. It then lies 8.5'

from Saturn and has no nearby

landmarks to point you in its

direction. It dims to 11th mag-

nitude by the time it passes 1.3'

north of the planet on the 22nd.

The solar system’s outermost

major planet is visible nearly all

night. Neptune stands 30°

above the southeastern horizon

as twilight ends in mid-October

and climbs halfway to the

zenith in the south around

10:30 p.m. local daylight time.

Although the ice giant dips low

42 ASTRONOMY • OCTOBER 2019

SKY THIS MONTH— Continued from page 37

EVENING SK Y

Mercury (southwest)

Venus (southwest)

Jupiter (southwest)

Saturn (south)

Uranus (east)

Neptune (southeast)

MIDNIGHT

Uranus (southeast)

Neptune (southwest)

MORNING SK Y

Mars (east)

Uranus (west)

Saturn’s outermost major moon reaches 10th magnitude in early October,
when it lies farthest west of the planet and its bright hemisphere faces Earth.

This visitor from the distant Oort Cloud should glow at 9th magnitude

in early October as it crosses from Pisces and Aquarius.

57

The number of years since Uranus appeared

so high in the Northern Hemisphere sky.