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Controversy over the Comets

Aug 19, 2015 - Aug 31, 2016

Galileo’s controversy over the comets illustrates how difficult it can be to implement novel research methods in science. 

Galileo believed that mathematics is the language of nature. He challenged the established discipline of natural philosophy, or physics, which used non-mathematical methods.

Galileo’s defenses of mathematics as the language of nature occurred in the midst of controversies with fellow mathematicians. Even for mathematicians, mathematical methods alone proved unable to resolve the enigmas they faced.  

History of Science

5th Floor Special Collections

This exhibit is located on the 5th Floor Special Collections, accessed through the elevators in the west main lobby of Bizzell Memorial Library. Visit History of Science for visitor information.

Exhibit At A Glance

1. Systems of the Universe

Earth-centered models of the universe, geocentric, and sun-centered models of the universe, heliocentric, equally predicted the position and movement of the planets. Given that the competing systems produced identical planetary predictions, astronomers searched for other kinds of observations that might decide between them. Comets seemed to cross through multiple spheres. The spheres of Mars and the Sun seemed likely to intersect. Several systems predicted that Venus might show phases. The Copernican system predicted stellar parallax, that stars should appear to slightly shift in position, which was not observed. Definitive evidence that could decide the true system of the universe proved elusive.

Athanasius Kircher, Ecstatic Journey through the Heavens (Iter exstaticum). Würzburg, 1660
Valentin Naibod, Principles of Astronomy (Astronomicarum institutionum). Venice, 1580
Christoph Clavius, Commentary on the Sphere of Sacrobosco (In sphaeram ionnis de Sacro Bosco commentarius). Rome, 1570
Louis Figuier, Galileo shows the satellites of Jupiter to the Venetian Senators. Paris, 1870
Bellarmine Robert, Robert Bellarmine, portrait
Tycho Brahe, Instruments for the Restoration of Astronomy (Astronomiae instauratae mechanica). Nuremberg, 1602
Tycho Brahe, Astronomical Letters (Epistolarum astronomicarum). Uraniborg, 1596
Tycho Brahe, Complete Works (Opera omnia). Frankfurt, 1648
Simon Mayr, The World of Jupiter (Mundus iovialis). Nuremberg, 1614
Giuseppe Biancani, Sphere of the Universe (Sphaera mundi). Bologne, 1620
Nicolaus Reimarus Ursus, Astronomical Foundation (Fundamentum astronomicum). Strassburg, 1588
Giambattista Riccioli, The New Almagest, part 1 (Almagestum novum). Bologna, 1651
Giambattista Riccioli, The New Almagest, part 2 (Almagestum novum). Bologna, 1651
Gabriele Beati, The Three Spheres (Sphaera triplex). Rome, 1662
Nicolas Bion, The Use of Celestial and Terrestrial Globes, and Spheres, according to the different Systems of the World (L'Usage des Globes Caeleste et Terrestre, et des Sphaeres, suivant les diffaerens Systaemes du Monde). Paris, 1710

2. Comets

Since antiquity, comets had posed an enigma. They appear without warning. They do not stay within the Zodiac like the planets. They come from different directions. Their speed and brightness change radically. Their tails always point away from the Sun. Parallax was observed for the Moon but not for comets, which implied that comets are farther away than the Moon, contrary to Aristotle’s argument that comets are fiery vapors in the upper atmosphere.

Illustration and Description of the Incomparably Great Comet (Abbildung und Beschreibung deß wunderwürdigen unvergleichlichen Cometen). Nuremberg, 1680
Johann Hevelius, On Comets (Cometographia). Gdansk, 1668
Johann Hevelius, The Climactic Year (Annus climactericus). Gdansk, 1685

Explore the Topic

Supplemental resources for a rich educational experience

Copernican System
Learn more about the Copernican system in which the Sun is immobile at the center of the universe.
Tycho Brahe’s System
Learn more about Tycho Brahe, who built the large astronomical observatory of Uraniborg in Hveen.
Galileo's World Exhibit Guide
iBook companion to the Galileo's World exhibition
Gallery Book Lists
A list of all books in every exhibit (author/title/date).
Controversy over the Comets Book List
A list of all books in the Controversy over the Comets exhibit (author/title/date).