Astronomy

CONTENTS

Trips and

tours

Travel the world

with the staff of

Astronomy.

My Science

Shop

The perfect gift

for your favorite

science geeks.

News

The latest

updates from

the science and

the hobby.

Sky This

Week

A daily digest of

celestial events.

4 ASTRONOMY • SEPTEMBER 2017

22 COVER STORY
Puzzled by Pluto
Far from the inert ball of ice
many scientists expected, this
distant world boasts unique
landscapes, recent geological
activity, and a possible
underground ocean.
S. ALAN STERN

28
Cassini’s Grand Finale:
20 years in the making
From grazing Saturn’s rings to
disappearing into its swirling
atmosphere, this spacecraft’s final
days, hours, and minutes will be
fruitful ones. MICHAEL CARROLL

34
16 times we didn’t
find E.T.
For decades, humanity has been
searching for aliens. Here are
the false alarms. JOHN WENZ;
ILLUSTRATION BY THEO COBB

36

Sky This Month

An ice giant pinnacle.

MARTIN RATCLIFFE AND

ALISTER LING

38

StarDome and

Path of the Planets

RICHARD TALCOTT;

ILLUSTRATIONS BY ROEN KELLY

44

Ask Astro

How SETI searches.

46

Phantom planets

The wild and woolly menagerie

of ghost worlds that once

haunted the halls of astronomical

history. JOHN WENZ

50

The secrets of off-season

globular clusters

Target this list of two dozen

beautiful star cities, none of which

you’ll find in the old standbys

of Scorpius, Ophiuchus, or

Sagittarius! F. MICHAEL WITKOSKI

54

How Flagstaff is

preserving dark skies

A star party and world-leading

community are keeping the

hometown of Lowell Observatory

in the dark. CHRISTIAN

LUGINBUHL AND JEFFREY HALL

60

Fun at America’s

Darkest Sky Star Party

Several dozen people gathered

in a small town under a clear,

steady sky — all for the love of

astronomy. MICHAEL E. BAKICH

COLUMNS

Strange Universe 10

BOB BERMAN

For Your Consideration 16

JEFF HESTER

Secret Sky 20

STEPHEN JAMES O’MEARA

Observing Basics 64

GLENN CHAPLE

Astro Sketching 66

ERIKA RIX

Binocular Universe 68

PHIL HARRINGTON

QUANTUM GRAVITY

Snapshot 8

Astro News 12

IN EVERY ISSUE

From the Editor 6

Astro Letters 11

New Products 69

Advertiser Index 70

Reader Gallery 72

Breakthrough 74

FEATURES

SEPTEMBER 2017

VOL. 45, NO. 9

28

Astronomy (ISSN 0091-6358, USPS 531-350) is

published monthly by Kalmbach Publishing

Co., 21027 Crossroads Circle, P. O. Box 1612,

Waukesha, WI 53187–1612. Periodicals post-

age paid at Waukesha, WI, and additional

offices. POSTMASTER: Send address changes to

Astronomy, P.O. Box 62320, Tampa, Fla. 33662-2320.

Canada Publication Mail Agreement #40010760.

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NASA/JHUAPL/S

WRI

ON THE COVER

The huge nitrogen ice glacier

Sputnik Planitia on Pluto is one

of the many surprising features

revealed by New Horizons.

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