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Night Sky, SkyWeek, and ESSCO.SPECTRUM by Peter Tyson
Coming to Terms
IN COSMOLOGY, A CURIOUS RELATION is at play in the naming of
things: The simplicity of terms used as shorthand for cosmic phe-
nomena tends to be inversely proportional to how puzzling those
phenomena are. Take the lingo that crops up in our pair of cosmol-
ogy features in this issue, which concern Type Ia supernovae and
the universe’s expansion rate, respectively.
In her article on page 14, Shannon Hall discusses the single-degenerate sce-
nario and the double-degenerate scenario. Sounds like one bully in a schoolyard
versus two. We put such terms in italics as red fl ags: Warning, jargon! But those
two concepts simply refer to whether white dwarfs explode because of inter-
action with a companion star (single scenario) or with a second white dwarf
(double scenario).
In his feature on page 22, Govert Schilling mentions the period-luminosity
relationship. This mouthful just means that the more luminous a Cepheid pul-
sating star is, the more slowly it pulsates.
Metaphor can help us grasp the complex — and
coin more user-friendly terms. In these articles, you’ll
read about the tip of the red giant branch. Gravitational
lenses. Standard candles, which serve as rungs on the
distance ladder.
It’s when you get to the most baffl ing cosmic stuff
of all that our sobriquets become the most basic. A
child might as well have suggested them. Dark energy.
Dark matter. Big Bang. We don’t italicize those three
because everyone is familiar with them — even many
a child — yet cosmologists have more questions about
them than just about anything else.
As scientists strive to crack such bedrock myster-
ies, they grapple with others along the way. These include the two compelling
conundrums investigated in these features. Hall wonders: How many ways can
you skin a Type Ia supernova? That is, how many types of detonators can trigger
such catastrophic blasts? We don’t know, but it’s more than we’d thought.
Schilling, for his part, asks: Why do the world’s leading cosmologists come
up with two entirely different numbers for the Hubble constant, the current
expansion rate of the universe? It’s as if they watched the same Super Bowl yet
insist on two different fi nal scores, with each side having every reason to believe
its conclusion is the correct one.
There are no answers, or only partial answers, to these
questions. And that’s what fi res up scientists intent on
unraveling such enigmas — call them what you will.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 Tafreshi
ART & DESIGN
Art Director Terri Dubé
Illustration Director Gregg Dinderman
Illustrator Leah Tiscione
ADVERTISING
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Newsstand Sales Scott T. Hill, [email protected]4 JUNE 2019 • SKY & TELESCOPE
NASA/^ CXC
/^ U.^ T
EX
ASG299 is the colorful
remnant of a Type Ia
supernova, one kind of
standard candle.