ABSTRACT
Galileo’s telescopic discoveries in 1610 and 1613 and his 1632 Dialogue, in which a terrestrial physics compatible with motions of the earth was set forth in the language of laymen, gained for Copernicus’s heliocentric astronomy its first widespread understanding and acceptance. Modern cosmology began half a century later with the Newtonian synthesis of Galileo’s new physics and Kepler’s basic laws of planetary motions. To understand Galileo’s cosmology, it is important to realize that he was primarily a mathematician and a physicist, not an astronomer, nor a philosopher. Studies of motion and of mechanics occupied Galileo almost exclusively until 1609, when news of the invention of the telescope in Holland reached him. Galileo’s mature cosmology is more nearly an idealized form of the Copernican system than a causal account. In contrast, the astronomies of Copernicus, Tycho Brahe, Ursus, and Kepler were supposed to fit with the physics of Aristotle—an impossible condition.
