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Hi Sara, Ross et al,
My understanding is that a seasonal (or unequal) hour is a period of
time ('in the first hour' etc) and not an instant. It is never divided
up into minutes and so the time of 6 minutes after dawn must be
referring to a time in equal hours, most probably measured with an
astrolabe as you suggest.
Regards,
John
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------ Original Message ------
From: "Schechner, Sara" <sche...@fas.harvard.edu>
To: "Ross Sinclair Caldwell" <belmu...@hotmail.com>
Cc: "'sundial list sundials'" <sundial@uni-koeln.de>
Sent: Tuesday, 30 Jun, 20 At 21:20
Subject: RE: Time problem
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://scholar.harvard.edu/saraschechner>
http://chsi.harvard.edu/ <http://chsi.harvard.edu/>
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BSS Editor http://sundialsoc.org.uk/publications/the-bss-bulletin/
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