Copernican revolution (book)

The Copernican Revolution: Planetary Astronomy in the Development of Western Thought is a book written by Thomas S. Kuhn and published in 1957 by Harvard University Press.

Thomas S. Kuhn is the author of the epoch making Structure of Scientific Revolutions (1962), a book that develops a completely new philosophical view on science and scientists. Kuhn introduces in this work the concept of paradigm shift, a sudden change of outlook and theory forming that occurs during scientific revolutions. He presents the "normal scientist" as the solver of the sort of puzzles that are not unlike jigsaw puzzles. A reader who expects to see some of this renown philosophy foreshadowed in The Copernican Revolution, will be disappointed. The terms "paradigm" and "normal science"—key concepts in the Scientific Revolutions—do not appear in this book.

By the Copernican Revolution Kuhn means the period that more commonly is referred to as the Scientific Revolution (singular). This is a sharply defined period that begins with the publication of Copernicus' work De Revolutionibus Orbium Coelestium in 1543 and closes with the appearance of Newton's Philosophiae Naturalis Principia Mathematica in 1687.

Kuhn spends the first half of his book on the pre-Copernicus view of mankind on the cosmos and the second half of the book on the period of the Copernican revolution itself. His exposition starts with the Egyptians, goes from Antiquity through the Dark Ages and the Medieval Period up to Copernicus. In this first half of the book Kuhn describes Western Civilization's developing understanding of the cosmos consisting of the Sun, the Moon, the planets, surrounding stars, and, of course, the Earth at the center of all of this. When Kuhn arrives in his account of astronomical history at Copernicus, it is remarkable that he refers to the latter's replacement of the Earth by the Sun as the geometric center of the Universe (the shift from a geocentric to a heliocentric cosmos) as Copernicus' "innovation" not as his "revolution". One may argue that this underplays the importance of Copernicus' discovery, but it is consistent, as Kuhn prefers to call the whole 145 year period starting in 1543 as "Copernicus' revolution". Nevertheless, the book treats Copernicus' innovation: not the Earth but the Sun is in the center of the solar system, as a pivotal point in the development of cosmology.

Chapter 1 explains a good deal of astronomical theory. It treats the apparent motion of the Sun as seen from Earth and introduces concepts as winter/summer solstice and vernal/autumnal equinox. It explains the ancient Two-Sphere Universe (a term coined by Kuhn), a tiny spherical Earth at the geometric center of the large rotating sphere of the stars.

Chapter 2 deals with the planets (derived from the Greek word for "wanderer"). For the Greek and their successors the Sun was one of the seven planets (Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn). The book details how the retrograde motion of the planets is explained by epicycles, small circles that rotate uniformly about a point on the circumference of a second rotating circle, the deferent. This theory culminated in the writing of the Almagest by Ptolemy.

Chapter 3 gives an account of Aristotelian cosmology and world view. The universe is bounded by the spheres of the stars and its interior is filled with aether. Further Aristotle believed that there were fifty-five crystalline shells and that these shells embodied a mathematical system of seven homocentric spheres carrying the planets.