by Rene Roy
Cambridge University Press
978-1-108-41701-3 — Unveiling Galaxies
Jean-René Roy
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UNVEILING GALAXIES
The Role of Images in Astronomical Discovery
Galaxies are known as the building blocks of the universe, but arriving at this understanding
has been a thousand-year odyssey. This journey is told through the lens of the evolving use
of images as investigative tools. Initial chapters explore how early insights developed in
line with new methods of scientiic imaging, particularly photography. The volume then
explores the impact of optical, radio, and X-ray imaging techniques. The inal part of the
story discusses the importance of atlases of galaxies; how astronomers organised images in
ways that educated, promoted ideas, and pushed for new knowledge. Images that created
confusion as well as advanced knowledge are included to demonstrate the challenges faced
by astronomers and the long road to understanding galaxies. By examining developments in
imaging, this text places the study of galaxies in its broader historical context, contributing
to both astronomy and the history of science.
jean-rené roy is a retired astronomer who was a professor at Laval University, Québec,
Canada from 1977 to 2000. Since then he has served as Deputy Director and Head of Sci-
ence at the Gemini Observatory in Hawai’i and Chile and worked at the Large Facilities
Ofice of the National Science Foundation and inally at the Space Telescope Science Insti-
tute. He has done research on the Sun, the interstellar medium, and the evolution of gas-rich
galaxies. A new edition of his previous book, A Question and Answer Guide to Astronomy,
was published in 2017.
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Jean-René Roy
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“As one of the world’s leading astronomers, Jean-René Roy provides us with an insight-
ful and readable account of the use of images to distinguish between deep-sky objects,
such as nebulae and galaxies. What makes this an exceptional work is the level to which
Roy, as a practitioner, engages with historians of science in developing his rich account.
This engagement leads to a unique book, one that will be indispensable to understanding
the signiicant role played by images in the history of twentieth-century science.”
Omar Nasim, Universität Regensburg
“Unveiling Galaxies examines the role of ‘transformational images’ in the history of
astronomy. Images are a tool of discovery, and this book brings attention to the ground-
breaking images behind some of the greatest discoveries in astronomy. The book also
highlights the role of galaxy atlases in astronomy as well as the lives of the people who
made these images and how their work impacted the progress of astronomy. I found
that telling the story of the discovery of galaxies by focussing on iconic images is an
excellent approach to the subject. Unveiling Galaxies is informative, well written, and
well researched, and provides a superb read of the process of discovery in science.”
Ronald J. Buta, University of Alabama
“In this beautifully clear, relective, and almost non-mathematical book, Jean-René Roy
explains how we came to understand that galaxies are the building blocks of the universe.
Roy is an accomplished galaxy researcher who takes us on this long and fascinating jour-
ney with its many challenges, from the perspective of developments in scientiic imaging
of galaxies. The story is based on images, starting with sketches of galaxies made from
visual observations in the 18th and 19th centuries. The book describes how the gradual
improvement in the quality of the images led to the understanding that galaxies are very
distant objects, lying far outside the Milky Way.”
Kenneth Freeman, The Australian National University
“Roy’s unique contribution goes beyond tracing the development of making images of
galaxies to examine their compilation into atlases. Roy’s underlying motivation for this
work is personal; his own exploration of a gift of an atlas of galaxies sparked his interest
in science and astronomy. With the descriptions of the characters who contributed to
the progress of understanding galaxies, the author reminds us that science is a human
activity. This book touches on the highlights of how images proceeded from eye and
hand to photographic and lately electronic record.”
Nancy Levenson, Space Telescope Science Institute
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Cambridge University Press
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Jean-René Roy
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UNVEILING GALAXIES
The Role of Images in Astronomical Discovery
JEAN-RENÉ ROY
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Cambridge University Press
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Jean-René Roy
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DOI: 10.1017/9781108261104
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Jean-René Roy 2018
This publication is in copyright. Subject to statutory exception
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Library of Congress Cataloging-in-Publication Data
Names: Roy, Jean-René, author.
Title: Unveiling galaxies : the role of images in astronomical discovery / Jean-René Roy
Description: New York, NY : Cambridge University Press, [2018] |
Includes bibliographical references and index.
Identiiers: LCCN 2017023077 | ISBN 9781108417013 (alk. paper)
Subjects: LCSH: Astronomical photography. | Galaxies. | Astronomy.
Classiication: LCC QB121.R697 2018 | DDC 523.1/12 – dc23
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We may, therefore, well hope that many excellent and useful matters are
yet treasured up in the bosom of nature. Francis Bacon
To the memories of Allan Rex Sandage, Gérard de Vaucouleurs and
Halton Christian Arp
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Contents
Preface
page ix
Introduction
1
Part I
Images and the Cosmos
1 Viewing Heavenly Mist
17
2 Portraying Cosmic Whirlpools
34
3 From Celestial Snapshots to Photographing the Realm of Galaxies
59
A – Photographing “Nebulae,” Pioneering Celestial Photography
60
B – Photographing Myriads of Galaxies: The Golden Age of
Astrophotography
72
4 Portraying “Nebulae” for the Mind
92
Part II Images as Galaxy Discovery Engines
5 The One-Thousand-Year Journey
105
6 Galaxies in Focus
131
7 A Symphony of Waves
150
8 Imaging the Invisible
173
Part III Organizing the World of Galaxies
9 The Galaxy Classiication Play-Off
187
10 Atlases of Galaxies, Picturing “Island-Universes”
205
11 Atlases of Galaxies, Viewed by Their Users
233
Conclusion
247
Appendix
253
Bibliography
257
Index
270
Colour plates are to be found between pages 144 and 145.
vii
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Preface
Galaxies are the building blocks of the universe. They have been and continue to be extraor-
dinary objects for probing and understanding the universe, its origin and evolution. This
book is about galaxies, and about how images led to their discovery and contributed to the
understanding of their nature.
Held together by gravitation, galaxies are gigantic systems of stars and clouds of gas
and dust. They populate the universe in the billions. Extrapolating counts from the deepest
current observations by telescopes in space and on the ground, one estimates that there are
more than 200 billion galaxies in the observable universe. We belong to one of them, the
Milky Way, a typical large spiral galaxy: disk-shaped like a slightly inlated pizza, the Milky
Way hosts about 200 billion stars and measures more than 100,000 light-years across. Our
Sun is one of its numerous stars and is located at about 27,000 light-years from the center
of the giant whirlpool of stars, interstellar gas and dust. We have only become aware of our
cosmic geography in the last century.
About a hundred years ago, in the late 1910s and through the 1920s – a remarkable
decade – astronomers proved beyond doubt that our Milky Way was one of numerous giant
stellar systems, and that a multitude of similar “island-universes” were scattered at colossal
distances from each other. “Nebulae,” noticed by sharp eye telescope viewing all over the
sky during previous centuries, were found to be extremely numerous, at least millions in
number, and complex in their appearances, from mottled disk-shaped pinwheels to soft
spheroidals. The diversity of silhouettes and forms turned out to be a key to understand the
formation and evolution of galaxies. Probed by inquisitive astronomers with the modern
photographic equipment of the twentieth century, “nebulae” became galaxies and literally
opened the door to grasping the whole universe. Some say, we then found the universe.1
Getting there was a fascinating story.
From the irst viewing of a “nebula” in the tenth century to the time these foamy patches
in the sky were explained and understood, it took more than a thousand years. Why did it
take so long? Discovering galaxies and determining their nature was indeed a long path full
of obstacles, confusion, debates, conlicts and inally convergence. In this book I will re-tell
this arduous road and exhilarating venture. To do so, I will employ a speciic perspective:
1 M. Bartusiak, The Day We Found the Universe, New York: Vintage Books, 2010.
ix
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x
Preface
the role of viewing, drawing and photographing in iguring out the nature of nebulae, and
I will show how this long and time-honored imaging process has helped to bring out the
world of galaxies.
Why Images?
An image allows us to see things, to record and describe them, to prove that they exist
and to relect on them. Images can bring irrefutable pieces of evidence for a concept or
proof of the reality of a “thing.” One can count objects on an image, measure their shapes,
identify features and establish if they contain structures, then describe these. When images
are digitized, mathematical operations can be executed and quantitative information can be
extracted from them. With a large number of images at hand, one can compare and recognize
variations between objects. In some cases, such as it was with “nebulae” over the centuries,
we might not have a clue about what the “thing” is. Once it is understood, common trends
can be traced, “peculiar cases” can be identiied and orderly behavior inferred.
Scientists are illustrators. They learn by juxtaposing objects and images. Images then
provide an empirical basis for classiication, often a critical pre-discovery step, to under-
stand the nature of objects, “nebulae” and galaxies, in our case.2 Atlases are the juxtaposi-
tion of images. Scientiic atlases with their rich compendia of images become the pictorial
beacons helping us to navigate the natural world. I will explore why and how the great
atlases of galaxies of the past decades were put together. I will explain how these image
galleries helped to broaden our knowledge of the world of galaxies, how they inluenced
research programs and drove the
design and construction of new telescopes and cameras.
We read text; we read images. Scientiic images are not only powerful conveyors of
information but also a tool to share complex knowledge.3 Images also carry esthetic value.
They help to create enthusiasm and understanding. Images of astronomical objects can be
truly beautiful, esthetically abstract and amazingly representational.4 The popularity of the
Hubble Space Telescope is in great part due to an outstanding and successful educational
effort to explain and share particularly signiicant astronomical images with an audience
broader than the astronomer specialist using the facility.5,6
My approach and perspective in writing this book are those of a practitioner: it is
the viewpoint of someone who has observed and studied galaxies, taught and trained
students into learning what they are, helped in building instruments to image galaxies
and, inally, run a large observatory where major programs were conducted to explore
these prodigious sidereal objects. My career was ignited by a spark. As a teenager, I was
2 S. J. Dick, Discovery and Classiication in Astronomy, Controversy and Consensus, Cambridge: Cambridge University Press, 2013, pp. 233–276.
3 M. Lynch and S. Y. Edgerton Jr., Aesthetic and digital image processing: representational craft in contemporary astronomy, The Sociological Review, 1987, Vol. 35, pp. 184–220.
4 M. Benson, Cosmigraphics, Picturing the Universe Through Time, New York: Abrams, 2014.
5 E. Snider, The Eye of Hubble, Framing Astronomical Images, Frame: A Journal of Visual and Material Culture, Issue One, Spring 2011, pp. 3–21.
6 For example, see Z. Levay, Hubble Space Telescope: Re-imagining the Universe, TEDxKC, 2015, www.youtube.com/watch?
v=JDJsiEI_0gE
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xi
dazzled and inspired by The Hubble Atlas of Galaxies by Allan Rex Sandage, a giant of
twentieth-century astronomy.
To ground my story on a broad foothold, I also borrow the works of scholars who have
