The Starry Universe of Johannes Kepler

TL;DR

This paper explores Johannes Kepler's conceptualization of the universe, emphasizing his view of stars as enormous, dim entities that supported the Copernican model and reflected divine power, contrasting with later astronomical findings.

Contribution

It analyzes Kepler's writings to understand his perception of stars and the universe, highlighting his support for the Copernican system based on observable star sizes.

Findings

Kepler viewed stars as larger than Earth's orbit

Kepler's universe reflected divine power and supported Copernican theory

Later 17th-century discoveries redefined star sizes and universe models

Abstract

Johannes Kepler described the Copernican universe as consisting of a central, small, brilliant sun with its planetary system, all surrounded by giant stars. These stars were far larger than, and much dimmer than, the sun -- his De Stella Nova shows that every visible star must exceed the size of the Earth's orbit, and the most prominent stars may exceed the size of the entire planetary system. His other writings, including his response to Ingoli, his Dissertatio cum Nuncio Sidereo, and his Epitome Astronomiae Copernicanae, also reflect this Copernican universe. To Kepler, such a universe was an illustration of divine power -- and solid evidence against the stars being suns, against the universe of Giordano Bruno. Kepler's starry universe was in fact the Copernican universe supported by observations of the stars, which showed them to have measureable apparent sizes. Not until the later seventeenth century were those apparent sizes shown to be spurious, allowing for a universe in which the stars were suns.