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Session 35 - HAD III: From Hamlet to Crop Circles.
Oral session, Wednesday, January 07

[35.05] Astronomy in the Age of Leonardo.

B. L. Welther (Harvard- Smithsonian CfA)

In the 1450s, when Leonardo da Vinci was born, horoscopes were still based primarily on the 13th-century tables developed in the court of Alfonso el Sabio of Spain. By the 15th century European astronomers were computing revised forms of the tables. In Italy, for example, Giovanni Bianchini of Ferrara completed his Tabulae astronomicae in the 1440s. It was finally published posthumously in Venice in 1495. By the 1480s Domenico Maria Novara, a professor of astronomy in Bologna, was publishing annual prognostications of eclipses, conjunctions, and other celestial phenomena.

Against this background of traditional astronomy in Italy, two Florentines recorded observations of the sun and moon, comets, and meteorology. Paolo dal Pozzi Toscanelli flourished in the first half of the 15th century and Leonardo da Vinci in the last half. Their observations of celestial phenomena were not primarily for astronomical purposes; they were spinoffs of other pursuits such as medicine, astrology, optics, engineering, and studies of light and shadow.

As a physician and cartographer, Toscanelli practiced astrology, studied omens, observed comets and plotted their paths on homemade maps. He also was associated with the construction of a gnomon at the top of the Duomo to observe the summer solstice. It was this project that may have brought him into contact with the young artisan, Leonardo da Vinci.

As a painter, Leonardo's approach to science and engineering was to observe, sketch and analyze. His interest in light and shadow led him to notice how the earth, moon and planets all reflect sunlight. His extant manuscripts have geometric sketches for eclipses and for the phenomenon known as "old moon in new moon's arms." Unfortunately, because neither Toscanelli nor Leonardo published their observations, they made no impact on the history of astronomical thought or observation. Their contemporaries did not know or write about their work. Astronomers in the 16th century did not know about their manuscripts.

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