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| Pair of shutters in Vatican Museum (Pascal Hilkens) |
This pair of painted shutters pertaining to the original windows of the "Sundial Gabinet" show a list of days, months,sun diameter and the time the sun takes to pass across the sundial in seconds and minutes.
This of course took my interest and I started to make my own calculations in order to compare with the data on the shutters. The easiest formula I found :
Time (seconds) to pass across the meridan line = 128 / cos(delta)
delta = declination of the sun at a specific day = cos ((360/365)*(N+10))*-23.7333
N = day of the year starting at january 1
The results of both my calculation as of the shutters are shown in the graph below and are quit comparable.
The below marble sundial with bronze inlays was originally embedded in the pavement of the Vatican "Sundial Gabinet" which was the apartment of Cardinal Librarian Francesco Saverio de Zelada (1717-1801) who live here from 1780 till 1798. Only this piece did survive.
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| Marble Sundial Vatican Museum (Pascal Hilkens) |
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| Cardinal de Zelada by Anton Raphael Mengs (source wikipedia) |
