The cosmological revolution of the seventeenth century saw the establishment of physics and astronomy as autonomous spheres. The Ptolemaic universe was a hierarchy of dignity – sun and stars above, lowly earth at the bottom – supported by a hierarchy of disciplines that set theology and metaphysics at the apex of intellectual life. The advancing belief in heliocentrism that undid the first was paralleled by challenges to the second, starting with the humanist celebration of rhetoric and moral philosophy and carried further by Copernicus’s exaltation of astronomy, hitherto assigned the lowly place of a mere computational aid, as a source of truth. The authority of the Church was often restricted by political and cultural divisions, so that many heretical ideas could not be stamped out, and Galileo long found support from Jesuits and even the pope. As he lost it, he sought backing in a wider audience, publishing his writings in Italian rather than Latin, and in a popular style. Newton and his followers would similarly seek to substitute horizontal connections for the vertical ones around which intellectual life had long been organized, demonstrating elements of their theories to popular audiences and explicitly describing the kind of science they favored as “public.”

It has long been recognized that astronomy was a catalyst of the Scientific Revolution, spurring on deeply consequential speculation about the nature of the cosmos and its physical principles. Yet the history of celestial physics is far richer than was thought a generation ago, and there is much to be learned about the origins of the field, particularly in the sixteenth century, when humanist activity brought forth a dazzling array of philosophical possibility—from reconsiderations of Aristotle and Islamicate commentary to the revival of Platonic, Epicurean, and Stoic worldviews. Celestial physics offered some of the most heated arguments for or against the Aristotelian cosmos, with controversial attempts to account for astronomical observation by integrating various causal innovations. This chapter will focus on a number of themes that mark celestial physics and cosmological speculation in the sixteenth and early seventeenth centuries: the order of the celestial bodies and their nature, the relationship between celestial and terrestrial things, the question of celestial animism or vitalism, and the status of the divine in celestial nature.