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Johannes Kepler protiv Frane Petrića: pitanje o ontologiji neba i kretanjima nebeskih tijela

The last quarter of the sixteenth century witnessed a radical shift in the understanding of the ontology of the heavens thanks (mostly) to Tycho Brahe, who – on the basis of studying the comets and nova – established that the machina coeli is » ; ; fluid« ; ; and that it cannot be a set of solid spheres. Thycho's theory of » ; ; liquid heavens« ; ; was more or less accepted by all astronomers, his assistant Johannes kepler included. In his book Nova de universis philosophia (1591) Frane Petrić also submitted his speculations about non-existence, of the solid heavenly spheres. Despite this common position, Kepler in his Apologia pro Tychne contra Ursum (1600) criticized Petrić and his explanation of planetary motions. According to Petrić, the planets – reasonable, intelligent and divine beings with soul – are freely moving in the liquid ether in the same way as they appear to us: in non-uniform spirals. Besides solid spheres, petrić apparently also rejects the postulate of the astronomy before kepler's Astronomia nova (1609), by which all heavenly bodies in reality (and contrary to what we see in the skies) move in uniform circles. According to Kepler, who agrees with petrić that planetary motions is ruled by the highest reason – i. e. God, God could bring about the planets to move as they appear to us – in spirals, but holds in far more reasonable that He regulated their paths in uniform circular motion. Petrić naively relies on the sense of sight and does not take into account the principle of optical relativity of apparent motion.

Kepler; Petrić; gibanja nebeskih tijela; ontologija neba

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