Sky & Telescope - July 2020 - 4
SPECTRUM
by Peter Tyson
The Caprice of Comets
The Essential Guide to Astronomy
Founded in 1941 by Charles A. Federer, Jr.
and Helen Spence Federer
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EDITORIAL
Editor in Chief Peter Tyson
Senior Editors J. Kelly Beatty, Alan M. MacRobert
Science Editor Camille M. Carlisle
News Editor Monica Young
Associate Editor Sean Walker
Observing Editor Diana Hannikainen
Consulting Editor Gary Seronik
Editorial Assistant Sabrina Garvin
Senior Contributing Editors
Dennis di Cicco, 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
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SE A N WA LK ER / MDW SK Y SURV E Y
ered comet, no matter how glorious its prospects appear to be, it's:
"Wow, this could be the comet of the century!" Whether or not
you believe in tempting fate, it's a fool's errand. Too many hypedup comets en route to the inner solar system have fi zzled, like winter's much-anticipated first snowstorm arriving as rain. Their very names stick
in the craw of dedicated comet lovers: Kohoutek. Austin. ISON.
"But some have turned out to be phenomenal," you might counter. True
enough. Names of those comets also remain fi xed in the minds of those who
treasure these dirty snowballs from afar. Bennett. West. Hyakutake. Hale-Bopp.
The uncertainty inherent in comet outcomes puts an astronomy magazine
like S&T in a bind. We don't want to miss the boat, but we don't want to go
down with a sinking ship either. So, as we were putting this issue together, we
asked ourselves: How should we deal with the latest Comet ATLAS?
Discovered on December 28th by the robotic Asteroid Terrestrial-impact Last
Alert System survey, Comet ATLAS (C/2019 Y4) will
reach perihelion on May 31st. We knew that would
be just after subscribers receive this issue.
So, we wondered, should we continue with our
plans to make this our comet issue? If ATLAS turned
out to be another "Great Comet," it would be fabulous timing to have this edition arriving in mailboxes
and on the newsstand just as ATLAS blossomed.
Comet ATLAS as seen at
But what if it wilted?
about 5:52 UT on April 15th
In the end, we decided to keep to comets. We start
with a news story about the interstellar comet 2I/Borisov (page 8). Ken HewittWhite then reminisces about the mid-1990s Hale-Bopp, the last "Great" comet
viewable from the Northern Hemisphere (page 30). Gerald Rhemann, who took
the cover shot, provides valuable tips on comet astrophotography (page 36). And
Paul Signorelli describes the sneaky way he retrieved his stolen astrocamera just
in time to capture Comet Halley on its return in 1986 (page 84).
We knew, though, that we had to play it safe with ATLAS. And lo and behold,
in mid-April as I write this, the comet has begun to fragment. To the ancient
Greeks, Atlas, the Titan condemned to shoulder the celestial sphere for eternity,
was a symbol of endurance. But poor Comet ATLAS may not last much longer.
It's one of the paradoxes of comets: After hurtling through space for billions
of years, they can fall apart within days. The tipping point comes after they
cross the so-called snowline about 3 a.u. from the Sun,
when their water ice begins to vaporize.
So let's just called ATLAS a comet and not the comet,
shall we?
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At-Large Trustees Tereasa Brainerd, Boston University;
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Sky & Telescope - July 2020
Table of Contents for the Digital Edition of Sky & Telescope - July 2020
Contents
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