logo Museo Galileo - Institute and Museum of the History of Science

The Two Ways of Astronomical Observation

Toward the end of the 16 th century cosmology and astronomy were, as they had been traditionally, two distinct disciplines. The former concerned the definition of the physical structure of the Universe, and was the province of philosophers. The latter aimed instead to record the positions of the heavenly bodies, and was the realm of mathematicians. To maintain the dual social function of astronomy - determining the calendar accurately and predicting the positions of the planets for drawing up horoscopes - the mathematical astronomers had developed over the centuries a set of graduated measurement instruments to be used by the naked eye.

Such outstanding figures as Nicolaus Copernicus (1473-1543) and Tycho Brahe (1546-1601) had already tried to resolve the dichotomy between cosmology and astronomy, and to define the structure of the Universe through accurate observations; but it was only the invention of the telescope that merged the two fields of knowledge materially. The telescope - a non-graduated instrument that revealed the true nature of the stars - introduced an entirely new mode of observing the sky. This premise is indispensable for understanding the colossal impact the instrument was to have on seventeenth-century science and society.

Portrait of T. Brahe (Astronomiae Instauratae Progymnasmata, 1610) T. Brahe, Astronomical sextant (W.J. Blaeu, Cosmographie Blaviane, 1667) O. Leoni, Portrait of Galileo, early 17th c. (Biblioteca Marucelliana, Firenze) G. Galilei, Presentation telescope, c. 1610 (IMSS, inv. 2428)
 ŠIMSS 2008 P.zza dei Giudici 1 50122 Florence P.I. 01346820481