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SkyWatch, Scanning the Skies,
Night Sky, SkyWeek, and ESSCO.SPECTRUM by Peter Tyson
A Feast for the Eyes
FORTUNATELY FOR ASTRONOMY, light comes in many fl avors. If
we could observe celestial objects and events only in the visible
light our eyes can perceive, we’d miss so much of what is on offer
out there. It would be like tasting only sweet foods but not salty,
bitter, sour, or savory. How limited our palate would be!
But what our eyes can’t picture, our instruments can. They can capture and
focus low-energy radio, microwave, and infrared photons as well as high-energy
ones such as ultraviolet, X-rays, and gamma rays. Through our ingenuity, light
from the entire electromagnetic spectrum has become viewable to us.
X-ray astronomy, for one, has come leaps and bounds since its start in the
early 1960s, as News Editor Monica Young details in our cover story on page 14.
One striking measure of this is that, between the launch of the fi rst focusing
X-ray telescope aboard a sounding rocket in 1965, and the launch of the Chan-
dra X-ray Observatory in 1999, the sensitivity of
X-ray telescopes improved 100 million times.
X-rays are emitted when matter has been heated
to temperatures in the millions of degrees, or
when particles have been accelerated to relativistic
speeds. By allowing us to “see” this high-energy
light, X-ray space telescopes like NASA’s Chandra
and the European Space Agency’s XMM-Newton —
both 20 years old this year — enable us to witness
events and objects in some of the universe’s most
extreme environments.
We can discern, for example, multi-million-
degree gas strands around ultra-dense neutron
stars or stellar black holes, whose wickedly strong gravity has yanked the gas
from a companion star. We can see the crescent-shaped shock front from a
supernova, where the force from what was an unimaginably violent explosion
has compressed interstellar gas so quickly as to leave it glowing in X-ray light.
X-ray astronomy helps us address fundamental questions. One example
involves the superhot gas that permeates galaxy clusters, the largest structures
in the universe. Studying these nebulous forms aids astronomers in tackling
what Riccardo Giacconi, the father of X-ray astronomy who died in December,
called “one of the most interesting open questions of modern cosmology” —
namely, how structure developed and evolved in the early universe.
X-rays can shoot right across the cosmos, yet Earth’s atmosphere absorbs
them. Imagine: After traveling for millions of years, they’re
stopped at the last nanosecond! But we get around that
barrier with X-ray space telescopes, which spread out a
celestial smorgasbord for our delectation and investigation.
Editor in ChiefThe Essential Guide to Astronomy
Founded in 1941 by Charles A. Federer, Jr.
and Helen Spence Federer
EDITORIAL
Editor in Chief Peter Tyson
Senior Editors J. Kelly Beatty, 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 SadlerSenior Contributing Editors
Robert Naeye, Roger W. SinnottContributing 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. WoodContributing Photographers
P. K. Chen, Akira Fujii, Robert Gendler,
Babak TafreshiART & DESIGN
Art Director Terri Dubé
Illustration Director Gregg Dinderman
Illustrator Leah Tiscione
ADVERTISING
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F+W MEDIA
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Newsstand Sales Scott T. Hill, [email protected]4 AUGUST 2019 • SKY & TELESCOPE
X-RAY
:^ NASA^ /CXC^ /UNIVERSITYO
F^ MICHIGAN^ /J-
T^ LI^ ET^ AL,^
OPTICAL
:^ NASA^ /STSCIIn this composite image of
the galaxy NGC 3079, X-rays
appear in pink and purple
and optical data in orange
and blue.