Astronomical Images : The Brunian hypothesis

Johannes Kepler

Astronomical Images

<p style='text-align: justify;'>Johannes Kepler's <i>Epitome astronomiae copernicanae</i> was published in three successive parts from 1617 to 1621. Intended as a new astronomical textbook for students, the <i>Epitome</i> covered much of the material traditionally associated with the <i>Theoricae planetarum</i> and works on spherical astronomy. Despite its title, the <i>Epitome</i> does not draw its information directly from Copernicus' <i>De revolutionibus</i> but is an original synthesis, mainly based on Kepler's own earlier works. It thus presents a comprehensive survey of Kepler's new astronomy. The text is illustrated by an abundance of images, with some figures printed multiple times. This image is presented in book 1 of the <i>Epitome</i> and serves to refute the theory of an infinite universe as proposed by Giordano Bruno. Though this refutation had first been developed by Kepler in his 1606 <i>De nova stella</i>, it was only in the <i>Epitome</i> that he employed illustrations to help demonstrate his arguments. This illustration utilises the simplified cosmological diagram presented by Kepler elsewhere in the book, depicting a central Sun surrounded by the orbit of the Earth and the sphere of the fixed stars. Here, this system is surrounded by an infinite space occupied by numerous fixed stars. The picture highlights the strangeness and singularity of the immense cavity containing our Sun and planets: a vast spherical space, nearly empty, surrounded by an 'army' of innumerable stars, comparatively close together. As one of Bruno's key concepts was 'homogeneity', this stark contrast was obvious and served to demonstrate the absurdity of the theory.</p>