The mercury horoscope of marcantonio Michel of Venice: A study in the History of Renaissance astrology and astronomy

Abstract

A statuette of Mercury (1527) wrought by Antonio Minelli and consecrated by a Venetian patrician, Marcantonio Michel, carries a horoscope combined with a graphic demonstration of the planet Mercury;s motion according to the Ptolemaic system. The first part of the study deals with the dating and astrological significance of the horoscope proper. It is shown that a uniquely proportious moment: 15th June, 1527, 8 a.m., was chosen to mark some important events in Michel's life. Judging from the general character of the horoscope, it is likely that it was destined to mark the conception of Michel's first child. As his son Vettore was born only 7 months later, the possibility of a premature birth must be envisaged. The concluding note (at end of study) evidences that the data of the horoscope were directly taken from Johannes Stöffler's ephemerides for the years 1499–1531. The second part of the paper discussed the history and development of Ptolemy's theory o f Mercury. In a degression the algebraic curve described by the centre of Mercury's epicycle is analysed. It is shown that this curve is practically interchangeable with the ellipse. The curve appears for the first time in a treatise by Azarquiel (eleventh century) which is preserved in a Spanish translation incorporated in the Libros Saber. European historians, with the exception of A. Wegener (1905), have failed to recognize the true significance of this curve, which is by no means and anticipation of Kepler's ellipse though it may have one of the stimuli that led to his experimenting with oval (elliptiform) curves. G. Peurbach (fifteenth century) almost totally depends on the Islamic astronomers' ( Azarquiel, Alhazen) interpretation of the Ptolemaic theory; he deals in extenso also with elliptiform curve. It is finally shown that the geometerical designs filling the interior of the horoscope were directly copied from Peurbach's Theoricae Novae Planetarum.