Sky & Telescope - November 2023 - 4

SPECTRUM by Peter Tyson
Outer Limits
IMAGINE LOOKING AT a free-floating ball of gas. What would you
see? Even if the gas had some color or texture to it, you might be
hard-pressed to tell where the surface of the ball begins and ends,
where exterior gives way to interior.
That's exactly our experience when observing the Sun (safely, of
course). Stars throw the whole concept of surface out of whack. A soap bubble
has more of a defined shell than our star does. Indeed, when we observe the
Sun, we're not so much looking at it as into it, albeit not very far.
Fortunately, while the Sun doesn't have a solid surface, it does have a visible
one, the photosphere. Serving as the base of the solar atmosphere, the photosphere
gives itself away - and aids us in delimiting the " surface " - by hosting
a range of distinctive phenomena. (See the stunning images on the cover and in
the corresponding feature on page 14.)
Among these phenomena are sunspots, those dark regions that resemble misshapen
sunflowers. A sunspot's black center, its umbra, and the wispy penumbra
that envelops it lend a sense of a horizontal layer to
what is otherwise ever-roiling plasma. Sunspot umbrae
are darker than their surroundings because they're
comparatively cooler: around 3700°C (6700°F) rather
than the predominant 5500°C (9900°F).
Outside of sunspots, most of the photosphere
A solar flare erupts
from the photosphere
in this image taken by
NASA's Solar Dynamics
Observatory.
consists of granules, which the Daniel K. Inouye Solar
Telescope, the subject of our cover story, captures better
than any telescope before it (see the dramatic image on
page 15). Looking like plasma popcorn, granules sheath
the Sun's entire visible surface, the " popped kernels "
each thousands of kilometers across.
The edge, or limb, of the Sun provides an alternate
sense of a covering, an impression enhanced by limb
darkening: When we look near the rim, we aren't peering
as deeply into the Sun as when we look at the middle. As such, we see only
the slightly cooler outer layers of plasma, which in turn appear slightly darker.
Other, loftier solar features also enhance our inkling of a surface from
which they arose. These include prominences, those dazzling flares of plasma
that extend from the photosphere right up to the corona.
Altogether, the solar spectacles transpiring in and above the photosphere
help us visually grasp the giant ball of gas that is our Sun. Without them, we'd
have a much harder time wrapping our heads around what
essentially doesn't have a wrapping.
Editor in Chief
Editorial Correspondence
(including permissions, partnerships, and content
licensing): Sky & Telescope, 1374 Massachusetts
Ave., 4th Floor, Cambridge, MA 02138, USA.
Phone: 617-500-6793. E-mail: editors@skyandtelescope.org.
Website: skyandtelescope.org. Unsolicited
proposals, manuscripts, photographs, and
electronic images are welcome, but a stamped,
self-addressed envelope must be provided to
guarantee their return; see our guidelines for
contributors at skyandtelescope.org.
4
Advertising Information:
E-mail Rod Nenner at: ads@skyandtelescope.org
Web: skyandtelescope.org/advertising
Subscription Rates:
U.S. and possessions: $57.73 per year (12 issues)
Canada: $73.18 (including GST)
All other countries: $88.63, by expedited delivery
All prices are in U.S. dollars.
The Essential Guide to Astronomy
Founded in 1941 by Charles A. Federer, Jr.
and Helen Spence Federer
EDITORIAL
Publisher Kevin B. Marvel
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, Richard Tresch Fienberg,
Roger W. Sinnott
Contributing Editors
Howard Banich, Jim Bell, Trudy Bell, Ronald Brecher,
Greg Bryant, Thomas A. Dobbins, Alan Dyer, Tony
Flanders, Ted Forte, 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, Fred Schaaf,
Govert Schilling, William Sheehan, Brian Ventrudo,
Mathew Wedel, Alan Whitman, Charles A. Wood,
Richard S. Wright, Jr.
Contributing Photographers
P. K. Chen, Robert Gendler, Babak Tafreshi
ART, DESIGN & DIGITAL
Creative Director Terri Dubé
Technical Illustrator Beatriz Inglessis
Illustrator Leah Tiscione
Web Developer & Digital Content Producer
Scilla Bennett
ADVERTISING
Director of Strategic Partnerships Rod Nenner
ads@skyandtelescope.org
AMERICAN ASTRONOMICAL
SOCIETY
Executive Officer / CEO, AAS Sky Publishing, LLC
Kevin B. Marvel
President Kelsey Johnson, University of Virginia
President-Elect Dara Norman, NOIRLab
Senior Vice-President Adam Burgasser, UC San Diego
Second Vice-President Grant Tremblay, Center for
Astrophysics, Harvard & Smithsonian
Third Vice-President Dawn Gelino, Caltech/IPACNExSCI
Treasurer
Doris Daou, NASA Planetary Science Division
Secretary Alice K. B. Monet, U.S. Naval Observatory (ret.)
At-Large Trustees Jane Rigby, NASA Goddard Space
Flight Center; Louis-Gregory Strolger, Space Telescope
Science Institute; B. Ashley Zauderer-VanderLey, National
Science Foundation; Lisa Prato, Lowell Observatory
Customer Service: Magazine customer
service and change-of-address notices:
skyandtelescope@omeda.com
Phone toll-free U.S. and Canada: 800-253-0245
Outside the U.S. and Canada: 847-559-7369
Mailing address: Sky & Telescope Magazine,
P.O. Box 219, Lincolnshire, IL 60069-9806, USA
Visit shopatsky.com
Shop at Sky customer service:
shopatsky.com/help
NOVEMBER 2023 * SKY & TELESCOPE
Newsstand and Retail Distribution:
Marisa Wojcik, mwojcik@i-cmg.com
Comag Marketing Group
The following are registered trademarks of
AAS Sky Publishing, LLC: Sky & Telescope
and logo, Sky and Telescope, The Essential
Guide to Astronomy, Skyline, Sky Publications,
skyandtelescope.org, skypub.org,
SkyWatch, Scanning the Skies, Night Sky,
SkyWeek, and ESSCO.
NASA / SDO
http://www.skyandtelescope.org/advertising http://www.skyandtelescope.org http://www.skyandtelescope.org http://www.skypub.org http://www.shopatsky.com http://www.skyandtelescope.org http://www.shopatsky.com/help
Sky & Telescope - November 2023

Table of Contents for the Digital Edition of Sky & Telescope - November 2023
