Chapter summary:
After the Chinese Ambassador had presented his power of attorney to Eugenius IV, he would have formally presented the Xuan De Astronomical Calendar, which would have established the precise date of the inauguration of the Emperor. Thousands of pieces of astronomical data were also included in the Chinese Ambassador’s calendar – to enable predictions of eclipses, the positions of sun, moon, planets and stars, future comets and times of sunrise and sunset.
In Toscanelli’s only surviving manuscript, a collection of folios, he includes a study of two comets – one in 1433, before the Chinese visit, and another in 1456, after the visit. Toscanelli’s observations of the first comet consist of a freehand drawing. He did not align the comet’s positions with any stars or planets. No times are listed, nor are right ascensions or declinations of the stars or comets. This is in stark contrast with Toscanelli’s treatment, 23 years later, of the 1456 comet. He uses a Jacob’s staff to give the comet’s altitude (declination) and longitude (right ascension) to within ten minutes of arc: times are now given, as are the declination and right ascensions of the stars (Chinese methods). To achieve this radical improvement in technique, Toscanelli must have had a clock, an accurate measuring device, astronomical tables and an instrument to show the position of the comet relative to stars and planets. This suggests a great leap in Toscanelli’s scientific capabilities
In 1475, Toscanelli had adopted a Chinese type of camera obscura, a slit of light and a bronzina (bronze casting) which he inserted in the lantern of the dome of Florence cathedral. By the early Ming dynasty, Zheng He’s astronomers had refined this camera obscura and used it in conjunction with an improved gnomon to enable measurement of the middle of the shadow of the sun within one-hundredth of an inch. Toscanelli used the Chinese method in a most ingenious way, adapting the dome of Santa Maria de Fiore to act as a solar observatory. In 1754, a Jesuit priest, Leonardo Ximenes, experimented with Toscanelli’s instrument. He found Toscanelli was able to determine not only the height of the sun at the summer solstice, but also the change in height over the years, which resulted from the change in the shape of the earth’s elliptical passage around the sun. The minute differences in the sun’s altitude from one year to another preoccupied Regiomontanus as well.
The exercises at Santa Maria del Fiore could be duplicated to observe the movement of the moon and produce equations of time of the moon. These, in turn, could be used in combination with the positions of stars and planets to determine longitude. Regiomontanus produced such tables and Columbus and Vespucci used them to calculate longitude in the New World. Diaz used Regiomontanus tables to determine the latitude of the Cape of Good Hope. Each of the instruments Toscanelli used in his observations at Santa Maria del Fiore – camera obscura, gnomon and clock – was used by Zheng He’s navigators, as were the instruments Toscanelli used to determine the passage of the 1456 comet – Jacob’s staff, clock and torquetum. All of Toscanelli’s discoveries — declination of the sun, obliquity of the ecliptic, passage of comets, ephemeris tables of the stars and planets — were contained in the 1408 Shou Shi. Toscanelli must have obtained his copious new knowledge of astronomy from the “distinguished men of great learning” who had arrived in Florence from China.
Further reading:
Lost discoveries by Dick Teresi – An excerpt on Chinese astronomy: http://www.readinggroupguides.com/guides3/lost_discoveries3.asp#excerpt
Churches as scientific instruments, by J. L. Heilbron
http://cis.alma.unibo.it/newsletter/090496Nw/heilbron.htm
The gnomon in the Cathedral of Santa Maria del Fiore:
http://www.cidaregioni.it/cidaregioni/it/Toscana/a_lo_gnomone_duomo_firenze.htm
