Sidereus Nuncius, or The Sidereal Messenger

By Galileo Galilei and Albert Van Helden

The “revolutionary, scintillating book” in which Galileo revealed his wondrous astronomical discoveries, with accompanying notes and historical context (Metascience).

Galileo Galilei’s Sidereus Nuncius is arguably the most dramatic scientific book ever published. It announced new and unexpected phenomena in the heavens, “unheard of through the ages,” revealed by a mysterious new instrument. Galileo had ingeniously improved the rudimentary “spyglasses” that appeared in Europe in 1608, and in the autumn of 1609 he pointed his new instrument at the sky, discovering astonishing sights: mountains on the moon, fixed stars invisible to the naked eye, individual stars in the Milky Way, and four moons around the planet Jupiter. These discoveries changed the terms of the debate between geocentric and heliocentric cosmology and helped ensure the eventual acceptance of the Copernican planetary system.

Albert Van Helden’s beautifully rendered and eminently readable translation is based on the Venice 1610 edition’s original Latin text. An introduction, conclusion, and copious notes place the book in its historical and intellectual context, and a new preface, written by Van Helden, highlights recent discoveries in the field, including the detection of a forged copy of Sidereus Nuncius, and new understandings about the political complexities of Galileo’s work.

• Language: English
• Publisher: Open Road Integrated Media
• Release date: Jan 19, 2016
• ISBN: 9780226320120

Book preview

SIDEREUS NUNCIUS

SIDEREUS NUNCIUS

or

THE SIDEREAL MESSENGER

GALILEO GALILEI

Second Edition

Translated and with Commentary by

ALBERT VAN HELDEN

THE UNIVERSITY OF CHICAGO PRESS

CHICAGO AND LONDON

GALILEO GALILEI (1564–1642) was an Italian physicist, mathematician, philosopher, and astronomer.

ALBERT VAN HELDEN is professor emeritus of history at Rice University and the University of Utrecht. He is translator and coeditor of On Sunspots, also available from the University of Chicago Press, and coeditor of The Origins of the Telescope.

The University of Chicago Press, Chicago 60637

The University of Chicago Press, Ltd., London

© 1989, 2015 by The University of Chicago

All rights reserved. Published 2015.

Printed in the United States of America

24 23 22 21 20 19 18 17 16 15 1 2 3 4 5

ISBN-13: 978-0-226-32009-0 (paper)

ISBN-13: 978-0-226-32012-0 (e-book)

DOI: 10.7208/chicago/9780226320120.001.0001

Library of Congress Cataloging-in-Publication Data

Galilei, Galileo, 1564–1642, author.

[Sidereus nuncius. English]

Sidereus nuncius or, The sidereal messenger / Galileo Galilei ; translated and with commentary by Albert Van Helden. — Second edition.

pages ; cm

Includes bibliographical references and index.

ISBN 978-0-226-32009-0 (pbk. : alk. paper) — ISBN 978-0-226-32012-0 (ebook) 1. Astronomy—Early works to 1800. 2. Jupiter (Planet)—Satellites—Early works to 1800. I. Van Helden, Albert, translator, writer of added commentary. II. Title. III. Title: Sidereus nuncius. IV. Title: Sidereal messenger.

QB41.G173 2016

520—dc23

2015019952

♾ This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper).

CONTENTS

PREFACE TO THE SECOND EDITION

PREFACE

INTRODUCTION

SIDEREUS NUNCIUS

CONCLUSION

THE RECEPTION OF SIDEREUS NUNCIUS

BIBLIOGRAPHY

INDEX

FOOTNOTES

PREFACE TO THE SECOND EDITION

Since the appearance of my translation in 1989, scholarship on this important moment in the history of science has undergone considerable development. First, Mario Biagioli’s Galileo, Courtier illuminated the social context of Galileo’s intellectual aspirations. How did natural philosophy, or what we would now call science, fare in the context of the absolutist Medici court? What strategies did Galileo employ both to improve his own social position and to gain authority for his arguments? Biagioli’s study taught us, for instance, how to decipher the rather flowery dedication of Sidereus Nuncius to Grand Duke Cosimo II of Tuscany, but it also explained more pragmatic puzzles, such as the author’s failure to send a copy of the treatise directly to the Imperial Mathematician at Prague, Johannes Kepler. Sidereus Nuncius had to be seen as carrying the authority of the absolute ruler of the state of Tuscany.¹

The origins of the telescope have also been clarified: it was the quality of the lenses that was the determining factor, and not, as I had earlier assumed, their strength alone. As Rolf Willach has brilliantly shown, the breakthrough came when a spectacle-maker, probably Hans Lipperhey of Middelburg, decreased the size of the aperture in a combination of lenses. This crucial and counterintuitive adaptation limited the incoming light to the central portion of the objective lens, where the quality of the curvature was highest.² In the meantime, the prevalence of eyeglasses and their manufacture, as well as the international trade in these commodities, has been documented by Vincent Ilardi in Renaissance Vision from Spectacles to Telescopes.³

We now know much more as well about the events in Padua in the summer of 1609, when Galileo made his first telescope. How Galileo went about improving a simple three-powered spyglass to turn it into a research instrument, teaching himself to grind and polish lenses, has recently been explained by Giorgio Strano. At stake here is a shopping list Galileo prepared late in 1609, listing glass, forms for grinding, and abrasive compounds, along with household staples such as lentils, chickpeas, and rice, and winter clothes for his infant son Vincenzo.⁴ These were busy days for Galileo: he had to give his lectures at the university, privately tutor the sons of noblemen in subjects such as fortifications, teach the students to use a proportional compass of his design, run a boarding house of sorts for some of these students, and spend endless, and often fruitless, hours grinding and polishing lenses. When time and weather permitted, he also devoted himself to inspecting the heavens through ever improved telescopes. His instrument-making and observing activities became more and more secretive in November and December, when he began his first telescopic research project, examining the surface of the Moon at a magnification of twenty. Others wanted lenses made by him; his own mother wrote furtively from Florence to one of Galileo’s servants, asking him to send her some of her son’s lenses. Galileo managed to stay ahead of the competition for at least a year; Eileen Reeves and I have shown how hard it was for others—in this case the mathematicians at the Jesuit Collegio Romano whose endorsement Galileo was to seek—to make telescopes as good as his and to verify his discoveries, if not all his interpretations.⁵

The lingering question of Galileo’s knowledge of optics, both theoretical and practical, has now been answered by Sven Dupré: there was widespread interest in Italy in devices for seeing distant objects, and along with his colleague Giovanni Antonio Magini at Bologna, and his friend Fra Paolo Sarpi in Venice, Galileo made a special study of mirrors with such a goal in mind. The hoped-for effect came not in the form of a device involving large mirrors, but rather a small tube with two mundane spectacle lenses.⁶ Dupré’s analysis is part of a more general focus on Galileo’s career in Padua before the telescope changed his life. Was he an engineer, a philosopher, an artist, or a professor, or did he somehow combine all these roles? In recent biographical studies, Galileo emerges as a member of important intellectual circles in Padua and Venice, a man interested not only in philosophy and practical mechanics, but also in language and the visual arts, a convinced Copernican who wanted little to do with Johannes Kepler’s public advocacy of that theory.⁷

The sequence of events surrounding Galileo’s unexpected discovery of Jupiter’s moons has been further elucidated by Owen Gingerich and myself.⁸ In the earth-centered cosmology, the Moon was one of the seven planets, fundamentally different from the Earth. The idea that there could be secondary celestial bodies circling these primary ones had never been considered. Such bodies would violate the fundamental principle of a unique center of rotation in the universe; the Earth occupied that position in the traditional cosmos, the Sun in the Copernican configuration. Although Galileo was a convinced Copernican, he had not entirely freed himself from the concepts and categories of the traditional earth-centered cosmology. He had initially found three, and soon four, new wandering stars on a straight line with Jupiter; their motion appeared wandering, or erratic, because they moved with respect to the background of the fixed stars. As Galileo soon discovered, the formation varied. They moved with respect to each other, and they kept pace with Jupiter in its orbit around the Sun, sometimes leading the planet and at other times lagging behind it. Were they somehow tied to Jupiter?

Fig. 1 shows Galileo’s notes for the first week of his observations. These can be found in the translation on pp. 66–70. Note Galileo’s efforts to make sense of these observations in the lower right-hand corner. The breakthrough came on January 13, the first time he saw all four bodies. In the worked-out log, the entry for that day reads: Having very thoroughly fastened the instrument [to a support], near Jupiter four stars were seen in this formation, or rather like this . After specifying the distances from Jupiter, he continues, they were not precisely in a straight line, as before, but the middle one of the three to the west [of Jupiter] was a little higher, or rather the westernmost one was somewhat lower.⁹ How could these bodies usually move back and forth in a straight line with respect to Jupiter, and yet from time to time one of them deviate from this line? Their motions with respect to Jupiter had to be individual, and the drawing shows a tilt to the entire configuration (fig. 2). Gingerich and I concluded that all of a sudden Galileo visualized four independent orbits in a plane ever so slightly inclined to his line of vision. He realized that he was observing four stars, or planets, going around Jupiter as it goes around the Sun, just as our Moon goes around the Earth as the Earth travels around the Sun. These were moons. At this moment a proper name, Moon, had become a term designating a category of heavenly bodies.

Figure 1. Draft of a letter from Galileo to the Doge of Venice, Leonardo Donato, August 1609, with Galileo’s first notes of his observations of Jupiter’s satellites. Courtesy of the University of Michigan.

Figure 2. The orbits of Jupiter’s satellites on 13 January 1610 and Galileo’s observation note of that day. The inclination of the orbital planes to the ecliptic has been increased for clarity. Courtesy of Owen Gingerich.

These original observations and the attempts to figure out the pattern of these new planets give some indication of Galileo’s style of visual thinking. Galileo’s hand was a trained hand, a skill he developed in Florence early in his life. Disegno, the skill of drawing and arranging objects in a drawing, was an important part of the education of a Florentine gentleman, and Galileo retained and referred to these precepts in perspective throughout his long career as an astronomer. Upon his return to Florence in 1613, Galileo became a member of the Accademia del Disegno. The best display of his skills can be found in his many drawings of the Moon in various phases, and a few years later in his study of sunspots. Horst Bredekamp has published an exhaustive analysis of Galileo as a draftsman and a visual thinker for whom text and image were very closely related, and for whom disegno was a tool for discovering the reality of nature.¹⁰ The broader context of Galileo’s relationship with painters, for instance Lodovico Cardi da Cigoli, has been laid out by Eileen Reeves, who shows how their interactions helped shape Galileo’s astronomy.¹¹

Sidereus Nuncius itself has, of course, not changed in 400 years, but we have learned much from recent research about the composition of the treatise. The initial section, not counting the dedication and the brief explanation of the telescope, dealing with the Moon, came first and had been at least partially written by the time Galileo discovered Jupiter’s moons.¹² The third section, devoted to those satellites, was printed while Galileo was still adding the last of such observations.¹³ As for the book’s title, to the question of whether nuncius should be translated as message or messenger (see the preface to the first edition), Nick Wilding has recently proposed a surprising answer: Galileo deliberately chose an ambiguous term.¹⁴

Sidereus Nuncius has been reprinted numerous times over the intervening four centuries, but to my knowledge it has never until recently been forged. In 2005 a very unusual copy of the first edition appeared on the rare book market. While it has long been known that some thirty copies of the original edition lacked their lunar etchings—an omission traditionally ascribed to the printer’s and author’s haste—this copy was adorned with drawings in the spaces reserved for those etchings. A plausible provenance was provided for this copy, and the intriguing possibility that Galileo himself had made the drawings was raised. If this were indeed the case, this copy would be worth millions. Historians of science and art were consulted, and the ensuing controversy lasted almost a decade, with historians lined up on both sides of the question. Persistent sleuthing by Nick Wilding slowly produced evidence that this copy was a brilliant forgery, and in 2013 a consensus was reached. By this time, the forger had been apprehended in Italy and was sentenced for related crimes, including the wholesale theft of valuable rare books from the Girolamini Library in Naples, of which he had been director.¹⁵ One very positive result of this episode is that Paul Needham has provided a brilliant, detailed account of the printing and makeup of Sidereus Nuncius, a study I hope will soon appear as a separate publication.¹⁶

In the first edition I indicated that the illustrations in Sidereus Nuncius were taken from the copy in the library of Wellesley College, but I did not mean this to include the diagrams of Galileo’s observations of Jupiter’s moons. These were taken instead from the facsimile edition that was published in Pisa to mark the 400th anniversary of Galileo’s birth. The original of that copy has been tracked down by Paul Needham: it is in the Brera Astronomical Observatory in Milan.¹⁷

Our Italian colleagues have published important works that bear on the subject of Sidereus Nuncius. Massimo Bucciantini’s Galileo e Keplero: Filosofia, cosmologia e teologia nell’Età della Controriforma (2000) deals in depth with the relationship between Galileo and Kepler. It is to be hoped this book, as well as Michele Camerota’s biography (note 7, above), will be translated into English soon. Recently Bucciantini and Camerota have joined forces with Franco Giudice to produce a detailed account of the reception of Sidereus Nuncius in different cultural settings in Europe. An English translation with the title Galileo’s Telescope: A European Story has recently been published.¹⁸ All these contributions, and much more, are reviewed in Eileen Reeves’s essay "A Decade of Historiography