Sky & Telescope - March 2019 - 4

SPECTRUM

by Peter Tyson

Super Stars

The Essential Guide to Astronomy
Founded in 1941 by Charles A. Federer, Jr.
and Helen Spence Federer

WITH THIS ISSUE we kick off a three-

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M A RCH 2 019 * SK Y & TELESCOPE

EDITORIAL
Editor in Chief Peter Tyson
Senior Editor Alan M. MacRobert
Science Editor Camille M. Carlisle
News Editor Monica Young
Associate Editors S. N. Johnson-Roehr, Sean Walker
Observing Editor Diana Hannikainen
Project Coordinator Bud Sadler
Digital Content Strategist Janine Myszka
Senior Contributing Editors
J. Kelly Beatty, Robert Naeye, Roger W. Sinnott
Contributing Editors
Howard Banich, Jim Bell, Trudy Bell, John E. Bortle,
Greg Bryant, Thomas A. Dobbins, Alan Dyer,
Tom Field, Tony Flanders, Ted Forte, Sue French,
Steve Gottlieb, David Grinspoon, Shannon Hall,
Ken Hewitt-White, Johnny Horne, Bob King,
Emily Lakdawalla, Rod Mollise, James Mullaney,
Donald W. Olson, Jerry Oltion, Joe Rao, Dean Regas,
Fred Schaaf, Govert Schilling, William Sheehan,
Mike Simmons, Mathew Wedel, Alan Whitman,
Charles A. Wood
Contributing Photographers
P. K. Chen, Akira Fujii, Robert Gendler,
Babak Tafreshi

ART & DESIGN
Art Director Terri Dubé
Illustration Director Gregg Dinderman
Illustrator Leah Tiscione
ADVERTISING
VP, Advertising Sales Kevin D. Smith
Advertising Sales Director Tim Allen
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N ASA / ESA / G. BACON (STSCI)

part series on famous stars: Polaris,
Alpha Centauri, and Betelgeuse.
Why did we choose these three over
the thousands of others visible to the
naked eye? Each holds abiding fascination not only
Artist's concept of the three-star
for astronomers, both amateur and professional, but
Polaris system
also for a broad swath of the enthusiastic public. Each
is iconic in its own way. And each provides a keyhole glimpse into different sectors of cutting-edge science, from the formation of planets to how stars explode.
Our first subject, Polaris, easily fits the bill. It's readily visible to observers
in the Northern Hemisphere, even in light-polluted skies. A fi xture of starparty outreach, it plays a fundamental role in familiarizing beginners with
the constellations. ("See those two stars on the outer edge of the Big Dipper's
bowl? They point to Polaris.") Owners of equatorial mounts generally rely on
the North Star to align their telescopes, and astrophotographers cherish it as a
centerpiece in their star-trails photos - just see our cover.
But Polaris's fame reaches beyond astronomy and into history and culture.
Generations of seafarers knew that the star indicates the direction to true
north, while its height in the heavens gives an idea of latitude. Our very notion
of the "lodestar," a guiding principle or person, arose from the navigational
utility of the North Star. Polaris became a lasting symbol of steadfastness: "I am
constant as the northern star," boasts Shakespeare's Julius Caesar, "Of whose
true-fi xed and resting quality / There is no fellow in the firmament."
The irony, as Camille Carlisle notes in our cover story starting on page 14,
is that "there is almost nothing constant about the North Star." Polaris is the
nearest and brightest Cepheid variable, those exquisitely precise pulsating stars
that serve as benchmarks for judging astronomical distances. Yet because of
quirks in its pulsation, Polaris is useless for this. Recently astronomers discovered that the star emits X-rays, which it shouldn't be able to do. Even the pole
star's much-vaunted fi xity is an illusion: After March 24th, 2100, the North
Star will begin moving away from the north celestial pole and will eventually
cease altogether serving as the Northern Hemisphere's lodestar.
Which brings me to the final criterion to be chosen for our series: A star had
to have personality. Polaris, that changeless changeling, certainly has it. And
each of the two others in our triad - Alpha Centauri (the nearest star system to
our own) and the red supergiant Betelgeuse (many people's favorite supernova
progenitor) - has its own distinct charisma. But you'll
have to wait till the April and May issues, respectively, to
get the skinny on them.

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Sky & Telescope - March 2019

Table of Contents for the Digital Edition of Sky & Telescope - March 2019

Contents
Sky & Telescope - March 2019 - Cover1
Sky & Telescope - March 2019 - Cover2
Sky & Telescope - March 2019 - 1
Sky & Telescope - March 2019 - Contents
Sky & Telescope - March 2019 - 3
Sky & Telescope - March 2019 - 4
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