Astronomical Images : The Earth has its centre of gravity, although it is not the centre of the World

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 offers an example of the iconographical innovation employed by Kepler in his <i>Epitome</i> and was used to demonstrate Kepler's conception of 'gravity'. In contrast to the Aristotelian account, which is refuted in the <i>Epitome</i>, Kepler asserted that levity and gravity are relative, rather than absolute, qualities. According to Kepler's account, each planet constituted a particular centre of gravity; thus the observation that heavy bodies fall (on Earth, for example) did not imply a position at the centre of the Universe. Represented diagrammatically in this image, the central spherical body represents any planet, while the black spots represent the heavy falling bodies that are attracted to this centre of gravity. The dotted lines represent light fumes and vapours, which do not float out to the extremities of the heavens but remain near the Earth because they do not possess 'absolute' levity.</p>