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Dear all, time ago this subject was the heart of an interesting discussion in the italian list of gnomonics. I remember that Gianni Ferrari asked to all if someone knew that problem because he was doing some adjustment to his software (I suppose). Many members send emails, someone saiyng 'yes' and someone saying 'no'. I tried to find the answere to the question posted by Gianni and I remember that I found a passage of a well known medieval author. Here is my little contribute to this debate, may be useful? ------------------------ Honorius from Autun (Honorius Augustodunensis) Writer of the first half of the XIIth cent. his life is totally ingnorated. Scholars attribute to him a lot of historical writings, theological, liturgical and enciclopedical not so much original but very spread out in the following centuries. He was an author accepted by the Roman Church and for that reason other authors not accepted used his name as their pseudonym. In concern the exact moment of the beginning of the day at the time of Honorius it is interesting the passage here quoted, that is locates in his book "Liber De Solis Affectibus," chap. XVI, 'De die et nocte'. In different texts of that period writers start to identify the day-light not more as the "presence of the sun onto the land" but as "presence of the light". Honorius himself , even if sometimes uses one, and sometimes the other definition, he is conscious of this clear difference, and then he mades this specifies. "Dies est sol lucens super terram, vel aer illuminatus, sed in æquinoctio ante solis ortum, et post solis occasum, aer est illuminatus, ergo nox non est æqualis diei. Sed notandum est, quod in talibus locutionibus per causam non attenditur natura rei expressæ: gnomonicæ enim arti studentes, ab umbra orientis, usque ad umbram insidentis (sic) horizonti, tantum diem numerant, et verum est, dum dies est, quando aer illuminatus est: sed aer et in lumine est antequam sit dies, per distinctionem horarum incipiat computari." Translation: "Day is said when the sun shines on the earth, that is when the sky (the air in the text) is lighted, but at the equinoxes, before the sun rises and after that it is set, the sky is still lighted, therefore the length of the night is not properly equal to that of the day. But it must be considered that with this 'way of say', we do not understand expressly the reality. Actually, peple that study the art of gnomonics they number the hours of the day starting from when the shadow moves from east up to when the shadow lies on the horizon (to othe west), and this is real, like it is day when the sky is light. But the atmosphere has lit up just before it begins the 'day' that we reckoning of the hours by the mean of the shadows." My translation isn't perfect but enough good to understand that Honorius seems to recognize three kind of meanings of the word 'day': the first one is practical, and is that the day actually appears for common people when the light is in the air, that is at twilight. The second one is tecnical, and reported to the gnomonists that consider 'day' only that part that one may quantify with the hours shown on a sundial. The tird one (that I didn't reported here) is the common definition of day as a total rotation of the eart (day plus night), that is the so called in medieval times 'natural day'. In the same book, at chap. XLVII, ' De ortu matutino et vespertino', we read the definition of three kind of sunset (and in opposite the sunrise). "Notandum quod alius ortus matutinus, alius vespertinus.
Matutinus, ubi aliqua stella orientem solem præcedit, post mediam noctem.
Vespertinus, ubi post occasus solis aliqua stella apparuit.
As far as I know since the sun limb is over the horizon the last shadow on the land can be measured, so probably Lucio isn't so far from truth, of course I understand that probably in medieval times in western cowntries they don't care about if it is in a way or in the other. Ciao Mario Arnaldi |
- center of the sun or not (to be or not to be) Mario Arnaldi
- Re: center of the sun or not (to be or not to be) Mario Arnaldi
