Kepler on the origin on comets : applying earthly knowledge to celestial events / Patrick J. Boner.
Abstract:
In De cometis libelli tres (1619), Johannes Kepler defined comets as ephemeral celestial phenomena originating from an ethereal aura whose essence was in many ways the same as that surrounding the Earth in the form of air. Kepler linked the celestial and terrestrial realms through common physical characteristics, comparing the origins, activities and eventual endpoints of comets with the corresponding attributes of earthly entities such as igneous outbursts and airborne projectiles. More fundamentally, Kepler relied in his 'earthly account' of comets on a common metaphysical foundation, in which phenomena in the celestial and sublunary spheres exemplified the same underlying mathematical principles. By means of these principles, Kepler claimed, the terrestrial realm realised the divine architectonic design originally implemented in the creation of the cosmos as a whole. These principles also explained how the sublunary world, in the form of the facultates animales of the Earth and its inhabitants, discerned and responded to astrological influences from the heavens. Kepler did not, however, intend to make astrological predictions the focal point for De cometis. Instead, he sought a more thorough natural knowledge of comets, in which mathematics, the metaphysical link between the celestial and terrestrial realms, was given a more prominent place in understanding the origins and interactions of earthly and heavenly phenomena
Nuncius Vol. 21, fasc. 1 (2006), p. 31-47