>>> In short, I am researching the biography of Filippo Maria Visconti >>> (1392-1447), duke of Milan, and you probably know that these Italian >>> princes relied heavily on astrology. So, Visconti's time of birth is known >>> precisely - "six minutes after sunrise," Monday, 23 September, 1392. His >>> natal chart was of course produced and interpreted, but it has been lost. I >>> am trying to recreate it as it might have been done by a court astrologer >>> of the time.<<<
I have some thoughts about ascertaining the time of "6 minutes after sunrise" in 1392 in Milan. First of all, Milan is one of the earliest towns to have a public tower clock in the 14th century, but it would only strike and show hours according to local solar time. It would not be divided into minutes. It was not reliable enough for such a horological chart. Sundials would be the more commonly used timepiece, but the six-minutes is an unusual amount of precision. My guess is that the court astronomer was using an astrolabe, which can be divided into units in the range of 4-6 minutes. Many also had arcs for the astrological houses and for both equal and unequal hours. The actual time might have been taken from a bright star still visible in the dawn. It is also worth considering what this 6-minutes after dawn really means. Is the astrologer using unequal hours which were still more common in these early days of clocks? If so, then six minutes would be equal to 1/10 of the first hour on that day of the year-i.e., 1/10 of 1/12 of the length of daylight. Lastly, in reconstructing a horoscope, one needs to know the position of the planets to place them on the chart. Some might be observed, but mostly they are taken from a table. These varied in different manuscript traditions. Do we have a clue what table the astrologer was using? Good luck with your project. Sara Sara J. Schechner, Ph.D. David P. Wheatland Curator of the Collection of Historical Scientific Instruments Lecturer on the History of Science Department of the History of Science, Harvard University Science Center 251c, 1 Oxford Street, Cambridge, MA 02138 Tel: 617-496-9542 | Fax: 617-495-3344 sche...@fas.harvard.edu<mailto:sche...@fas.harvard.edu> | @SaraSchechner http://scholar.harvard.edu/saraschechner http://chsi.harvard.edu/
--------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
