subject:"Time problem"

RE: Time problem

2020-07-01 Thread Ross Sinclair Caldwell

Thank you, Gian!

So it was in the "second part" of Maria Arnaldi's paper, that I stupidly did 
not read.

Perfect. I am very grateful.

Best regards,

Ross
43.349399 3.22422981
Béziers, France


De : Gian Casalegno 
Envoyé : mercredi 1 juillet 2020 18:13
À : Ross Sinclair Caldwell 
Cc : sundial list sundials 
Objet : Re: Time problem

You can find an explanation of the meaning of the hours "da campanile" i.e. "a 
half hour after" in :
https://www.academia.edu/2021256/Le_ore_italiane._Origine_e_declino_di_uno_dei_piu_importanti_sistemi_orari_del_passato_seconda_parte_
Regards,
Gian


Il giorno mer 1 lug 2020 alle ore 17:04 Ross Sinclair Caldwell 
mailto:belmu...@hotmail.com>> ha scritto:

To find some authority for the understanding that the Italian hours begin at 
the end of dusk, or about half an hour after sunset, I note that in the BBS 
Sundial Glossary under “hour plane” - “Italian” it says -


“there is some evidence in older works that Italian hours were counted from 30 
minutes after sunset.”

http://sundialsoc.org.uk/discussions/glossary-a-z/8/


Does anyone know what this evidence in older works is?


A few other places I've looked -


Wikipedia says “end of dusk, i.e. half an hour after sunset.”

https://en.wikipedia.org/wiki/Hour


This looked promising - Mario Arnaldi, Le ore italiane. Origine e declino di 
uno dei più importanti sistemi orari del passato (prima parte).

https://www.academia.edu/2021250/Le_ore_italiane._Origine_e_declino_di_uno_dei_piu_importanti_sistemi_orari_del_passato_prima_parte_


But he does not mention the notion of "a half hour after" (mezz'ora dopo) 
sunset  (tramonto del sole).


Ross Caldwell
43.349399 3.22422981
Béziers, France



De : sundial 
mailto:sundial-boun...@uni-koeln.de>> de la part 
de Ross Sinclair Caldwell mailto:belmu...@hotmail.com>>
Envoyé : mercredi 1 juillet 2020 16:41
À : John Davis 
mailto:john.davi...@btopenworld.com>>; Schechner, 
Sara mailto:sche...@fas.harvard.edu>>
Cc : 'sundial list sundials' mailto:sundial@uni-koeln.de>>
Objet : RE: Time problem

Hi John, Sara 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.
I agree. All that remains unknowable is the visibilty at the time. If it were 
overcast at dawn, they must have calculated rather than observed. But I tend to 
think it was observed, and determined with an astrolabe.

Ross

De : John Davis 
mailto:john.davi...@btopenworld.com>>
Envoyé : mercredi 1 juillet 2020 10:10
À : Ross Sinclair Caldwell mailto:belmu...@hotmail.com>>; 
Schechner, Sara mailto:sche...@fas.harvard.edu>>
Cc : 'sundial list sundials' mailto:sundial@uni-koeln.de>>
Objet : RE: Time problem

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

---



-- Original Message --
From: "Schechner, Sara" 
mailto:sche...@fas.harvard.edu>>
To: "Ross Sinclair Caldwell" mailto:belmu...@hotmail.com>>
Cc: "'sundial list sundials'" 
mailto: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

RE: Time problem

2020-07-01 Thread Ross Sinclair Caldwell

Hi Sara,

There will be local customs but the technical time, taken from the Latin 
description of the hours is that Italian hours were counted from sunset and 
Babylonian hours from sunrise.  There is no mention of dusk.

Indeed, I find that technical definition with no mention of dusk, but I also 
keep coming across the “half hour after” description as well, not only in the 
BBS glossary. This is the assertion of Dohrn-van Rossum that I am trying to 
find authority for, since he cites none (it is not in Galvano Fiamma, who only 
describes the clock in Milan in 1336).


In what is presumably the oldest Italian form of hour-reckoning, unequivocally 
attested for the first time by Galvano Fiamma, the twenty-four hours were 
counted through from one evening – more precisely: one half-hour after sundown 
– to the evening of the following day. The twenty-fourth hour was the last hour 
of daytime. The only linkage to daylight has to do with timing the point at 
which the counting begins in the evening.

(Gerhard Dohrn-van Rossum, History of the Hour: Clocks and Modern Temporal 
Orders (UChicago Press, 1996 (translation of Die Geschichte der Stunde: Uhren 
und moderne Zeitordnungen. München-Wien, Carl Hansen Verlag, 1992, p. 114))


So Riccardo Anselmi, in the “Piccolo glossario” to his sundial page ( 
http://sundials.anselmi.vda.it/ ) says, with you, “in some cases” it is half an 
hour after sunset -


Ore Italiche, sistema di suddivisione del tempo che viene misurato dal tramonto 
del sole o, in taluni casi, mezz’ora dopo il tramonto.


http://sundials.anselmi.vda.it/MyPage_GenericPage2_Italiano.htm


In the Italian wikipedia page for Ora italica, 
https://it.wikipedia.org/wiki/Ora_italica , they define Italian hours as the 
method by which


...la giornata era divisa in 24 ore della stessa durata, che venivano numerate 
a partire da mezz'ora dopo il tramonto (quando le campane suonavano l'Ave 
Maria).
So here it is connected to the bell ringing the Ave Maria prayer time (I have 
read elsewhere it was for the Angelus, or maybe they were synonymous, since the 
Angelus consists of three statements about the Annunciation each followed by an 
Ave Maria).

In the last paragraph of the page, they cite an episode in Alessandro Manzoni's 
1827 novel I promessi sposi, set in 1628, in which the character Renzo 
describes being awakened when the clock rang eleven times. The wikipedia 
editors calculate from his description that it was on 13 November, and go on to 
say that the sun set at 16:55 CET, or at 16:32 local time. A half-hour after 
this, around 17:00 local time, the bell would have rung the Ave Maria. 
Therefore “eleven strikes” means four in the morning our time.


So it would seem that Milan was one of those “sometimes,” or local places that 
used the half-hour after sunset, or end of dusk, rule.


Best regards,


Ross

43.349399 3.22422981
Béziers, France



De : Schechner, Sara 
Envoyé : mercredi 1 juillet 2020 17:41
À : Ross Sinclair Caldwell 
Cc : 'sundial list sundials' 
Objet : RE: Time problem


There will be local customs but the technical time, taken from the Latin 
description of the hours is that Italian hours were counted from sunset and 
Babylonian hours from sunrise.  There is no mention of dusk.



Sara Schechner

Author of Time of Our Lives: Sundials at the Adler Planetarium



From: sundial  On Behalf Of Ross Sinclair Caldwell
Sent: Wednesday, July 01, 2020 11:04 AM
Cc: 'sundial list sundials' 
Subject: RE: Time problem



To find some authority for the understanding that the Italian hours begin at 
the end of dusk, or about half an hour after sunset, I note that in the BBS 
Sundial Glossary under “hour plane” - “Italian” it says -



“there is some evidence in older works that Italian hours were counted from 30 
minutes after sunset.”

http://sundialsoc.org.uk/discussions/glossary-a-z/8/<https://urldefense.proofpoint.com/v2/url?u=http-3A__sundialsoc.org.uk_discussions_glossary-2Da-2Dz_8_=DwMF-g=WO-RGvefibhHBZq3fL85hQ=7ZsgDX5inZSMERqhZEQacOtdADP0iy6-YB7dx6Z_mVo=UVmfG-Lwit5L4Etra9dngAhE7-_MBgKCK6nhJjl2zNk=Otrt5JkuLSHGmLmV5ku8B4qjZc9bNH8XXWwN7M-P4s4=>



Does anyone know what this evidence in older works is?



A few other places I've looked -



Wikipedia says “end of dusk, i.e. half an hour after sunset.”

https://en.wikipedia.org/wiki/Hour<https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Hour=DwMF-g=WO-RGvefibhHBZq3fL85hQ=7ZsgDX5inZSMERqhZEQacOtdADP0iy6-YB7dx6Z_mVo=UVmfG-Lwit5L4Etra9dngAhE7-_MBgKCK6nhJjl2zNk=e9M1Wr7ky9nfDOfVM5T1hGV6XkG6oMzk2v92ms6AwfQ=>



This looked promising - Mario Arnaldi, Le ore italiane. Origine e declino di 
uno dei più importanti sistemi orari del passato (prima parte).

https://www.academia.edu/2021250/Le_ore_italiane._Origine_e_declino_di_uno_dei_piu_importanti_sistemi_orari_del_passato_prima_parte_<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.academia.edu_2021250_Le-5Fore-5Fital

Re: Time problem

2020-07-01 Thread Gian Casalegno

You can find an explanation of the meaning of the hours "da campanile" i.e.
"a half hour after" in :
https://www.academia.edu/2021256/Le_ore_italiane._Origine_e_declino_di_uno_dei_piu_importanti_sistemi_orari_del_passato_seconda_parte_

Regards,
Gian


Il giorno mer 1 lug 2020 alle ore 17:04 Ross Sinclair Caldwell <
belmu...@hotmail.com> ha scritto:

> To find some authority for the understanding that the Italian hours begin
> at the end of dusk, or about half an hour after sunset, I note that in the
> BBS Sundial Glossary under “hour plane” - “Italian” it says -
>
>
> “there is some evidence in older works that Italian hours were counted
> from 30 minutes after sunset.”
>
> http://sundialsoc.org.uk/discussions/glossary-a-z/8/
>
>
> Does anyone know what this evidence in older works is?
>
>
> A few other places I've looked -
>
>
> Wikipedia says “end of dusk, i.e. half an hour after sunset.”
>
> https://en.wikipedia.org/wiki/Hour
>
>
> This looked promising - Mario Arnaldi, *Le ore italiane. Origine e
> declino di uno dei più importanti sistemi orari del passato (prima parte)*
> .
>
>
> https://www.academia.edu/2021250/Le_ore_italiane._Origine_e_declino_di_uno_dei_piu_importanti_sistemi_orari_del_passato_prima_parte_
>
>
> But he does not mention the notion of "a half hour after" (*mezz'ora dopo*)
> sunset  (*tramonto del sole*).
>
>
> Ross Caldwell
> 43.349399 3.22422981
> Béziers, France
>
>
> --
> *De :* sundial  de la part de Ross Sinclair
> Caldwell 
> *Envoyé :* mercredi 1 juillet 2020 16:41
> *À :* John Davis ; Schechner, Sara <
> sche...@fas.harvard.edu>
> *Cc :* 'sundial list sundials' 
> *Objet :* RE: Time problem
>
> Hi John, Sara 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.
>
> I agree. All that remains unknowable is the visibilty at the time. If it
> were overcast at dawn, they must have calculated rather than observed. But
> I tend to think it was observed, and determined with an astrolabe.
>
> Ross
> ------
> *De :* John Davis 
> *Envoyé :* mercredi 1 juillet 2020 10:10
> *À :* Ross Sinclair Caldwell ; Schechner, Sara <
> sche...@fas.harvard.edu>
> *Cc :* 'sundial list sundials' 
> *Objet :* RE: Time problem
>
> 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
>
> ---
>
>
>
> -- Original Message --
> From: "Schechner, Sara" 
> To: "Ross Sinclair Caldwell" 
> Cc: "'sundial list sundials'" 
> 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 minu

RE: Time problem

2020-07-01 Thread Schechner, Sara

There will be local customs but the technical time, taken from the Latin 
description of the hours is that Italian hours were counted from sunset and 
Babylonian hours from sunrise.  There is no mention of dusk.

Sara Schechner
Author of Time of Our Lives: Sundials at the Adler Planetarium

From: sundial  On Behalf Of Ross Sinclair Caldwell
Sent: Wednesday, July 01, 2020 11:04 AM
Cc: 'sundial list sundials' 
Subject: RE: Time problem

To find some authority for the understanding that the Italian hours begin at 
the end of dusk, or about half an hour after sunset, I note that in the BBS 
Sundial Glossary under "hour plane" - "Italian" it says -

"there is some evidence in older works that Italian hours were counted from 30 
minutes after sunset."

http://sundialsoc.org.uk/discussions/glossary-a-z/8/<https://urldefense.proofpoint.com/v2/url?u=http-3A__sundialsoc.org.uk_discussions_glossary-2Da-2Dz_8_=DwMF-g=WO-RGvefibhHBZq3fL85hQ=7ZsgDX5inZSMERqhZEQacOtdADP0iy6-YB7dx6Z_mVo=UVmfG-Lwit5L4Etra9dngAhE7-_MBgKCK6nhJjl2zNk=Otrt5JkuLSHGmLmV5ku8B4qjZc9bNH8XXWwN7M-P4s4=>

Does anyone know what this evidence in older works is?

A few other places I've looked -

Wikipedia says "end of dusk, i.e. half an hour after sunset."

https://en.wikipedia.org/wiki/Hour<https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Hour=DwMF-g=WO-RGvefibhHBZq3fL85hQ=7ZsgDX5inZSMERqhZEQacOtdADP0iy6-YB7dx6Z_mVo=UVmfG-Lwit5L4Etra9dngAhE7-_MBgKCK6nhJjl2zNk=e9M1Wr7ky9nfDOfVM5T1hGV6XkG6oMzk2v92ms6AwfQ=>

This looked promising - Mario Arnaldi, Le ore italiane. Origine e declino di 
uno dei più importanti sistemi orari del passato (prima parte).

https://www.academia.edu/2021250/Le_ore_italiane._Origine_e_declino_di_uno_dei_piu_importanti_sistemi_orari_del_passato_prima_parte_<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.academia.edu_2021250_Le-5Fore-5Fitaliane.-5FOrigine-5Fe-5Fdeclino-5Fdi-5Funo-5Fdei-5Fpiu-5Fimportanti-5Fsistemi-5Forari-5Fdel-5Fpassato-5Fprima-5Fparte-5F=DwMF-g=WO-RGvefibhHBZq3fL85hQ=7ZsgDX5inZSMERqhZEQacOtdADP0iy6-YB7dx6Z_mVo=UVmfG-Lwit5L4Etra9dngAhE7-_MBgKCK6nhJjl2zNk=xS0qdc5Y2l8IIE79QlSnj2l2GWertLAFsRptNCGTxHk=>

But he does not mention the notion of "a half hour after" (mezz'ora dopo) 
sunset  (tramonto del sole).

Ross Caldwell
43.349399 3.22422981
Béziers, France

De : sundial 
mailto:sundial-boun...@uni-koeln.de>> de la part 
de Ross Sinclair Caldwell mailto:belmu...@hotmail.com>>
Envoyé : mercredi 1 juillet 2020 16:41
À : John Davis 
mailto:john.davi...@btopenworld.com>>; Schechner, 
Sara mailto:sche...@fas.harvard.edu>>
Cc : 'sundial list sundials' mailto:sundial@uni-koeln.de>>
Objet : RE: Time problem

Hi John, Sara 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.
I agree. All that remains unknowable is the visibilty at the time. If it were 
overcast at dawn, they must have calculated rather than observed. But I tend to 
think it was observed, and determined with an astrolabe.

Ross

De : John Davis 
mailto:john.davi...@btopenworld.com>>
Envoyé : mercredi 1 juillet 2020 10:10
À : Ross Sinclair Caldwell mailto:belmu...@hotmail.com>>; 
Schechner, Sara mailto:sche...@fas.harvard.edu>>
Cc : 'sundial list sundials' mailto:sundial@uni-koeln.de>>
Objet : RE: Time problem

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

---

-- Original Message --
From: "Schechner, Sara" 
mailto:sche...@fas.harvard.edu>>
To: "Ross Sinclair Caldwell" mailto:belmu...@hotmail.com>>
Cc: "'sundial list sundials'" 
mailto: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

RE: Time problem

2020-07-01 Thread Ross Sinclair Caldwell

To find some authority for the understanding that the Italian hours begin at 
the end of dusk, or about half an hour after sunset, I note that in the BBS 
Sundial Glossary under “hour plane” - “Italian” it says -


“there is some evidence in older works that Italian hours were counted from 30 
minutes after sunset.”

http://sundialsoc.org.uk/discussions/glossary-a-z/8/


Does anyone know what this evidence in older works is?


A few other places I've looked -


Wikipedia says “end of dusk, i.e. half an hour after sunset.”

https://en.wikipedia.org/wiki/Hour


This looked promising - Mario Arnaldi, Le ore italiane. Origine e declino di 
uno dei più importanti sistemi orari del passato (prima parte).

https://www.academia.edu/2021250/Le_ore_italiane._Origine_e_declino_di_uno_dei_piu_importanti_sistemi_orari_del_passato_prima_parte_


But he does not mention the notion of "a half hour after" (mezz'ora dopo) 
sunset  (tramonto del sole).


Ross Caldwell
43.349399 3.22422981
Béziers, France



De : sundial  de la part de Ross Sinclair 
Caldwell 
Envoyé : mercredi 1 juillet 2020 16:41
À : John Davis ; Schechner, Sara 

Cc : 'sundial list sundials' 
Objet : RE: Time problem

Hi John, Sara 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.
I agree. All that remains unknowable is the visibilty at the time. If it were 
overcast at dawn, they must have calculated rather than observed. But I tend to 
think it was observed, and determined with an astrolabe.

Ross

De : John Davis 
Envoyé : mercredi 1 juillet 2020 10:10
À : Ross Sinclair Caldwell ; Schechner, Sara 

Cc : 'sundial list sundials' 
Objet : RE: Time problem

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

---



-- Original Message --
From: "Schechner, Sara" 
To: "Ross Sinclair Caldwell" 
Cc: "'sundial list sundials'" 
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://chsi.harvard.edu/

__

RE: Time problem

2020-07-01 Thread Ross Sinclair Caldwell

Hi John, Sara 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.
I agree. All that remains unknowable is the visibilty at the time. If it were 
overcast at dawn, they must have calculated rather than observed. But I tend to 
think it was observed, and determined with an astrolabe.

Ross

De : John Davis 
Envoyé : mercredi 1 juillet 2020 10:10
À : Ross Sinclair Caldwell ; Schechner, Sara 

Cc : 'sundial list sundials' 
Objet : RE: Time problem

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

---



-- Original Message --
From: "Schechner, Sara" 
To: "Ross Sinclair Caldwell" 
Cc: "'sundial list sundials'" 
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://chsi.harvard.edu/


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Dr J Davis
Flowton Dials http://www.flowton-dials.co.uk/
BSS Editor 
http://sundialsoc.org.uk/publications/the-bss-bulletin/<http://www.sundialsoc.org.uk/bulletin.php>

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RE: Time problem

2020-07-01 Thread Ross Sinclair Caldwell


Hi Sara, thank you for your comments.

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. ... 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.
I agree that his astrologers would not have counted minutes by the clock. Venus 
was indeed far enough from the Sun to be clear at dawn, presuming it were a 
clear day.

Is the astrologer using unequal hours which were still more common in these 
early days of clocks?

I can't answer that with certainty. My guess would be equal hours, since 
astronomers had no practical use to distinguish between daylight and nighttime 
hours, but would want a consistent system throughout for their calculations.

I am sure I can find the answer, though.

Do we have a clue what table the astrologer was using?

We know the textbooks used at Pavia, where the first Lectureship of Astrology 
was established, so it should be easy to find out. Monica Azzolini, who has 
written on astrology in the time of Visconti and Sforza rule of Milan, compares 
modern values to the Alfonsine Tables when she discusses Galeazzo Maria 
Sforza's chart, so I assume that those tables were standard, and I won't go 
wrong using them. A Swedish physicist, Lars Gislén, has produced spreadsheets 
to calculate various pre-modern astronomical data, including by the Alfonsine 
Tables . His homepage http://home.thep.lu.se/~larsg/Site/Welcome.html
At "Download my applications," http://home.thep.lu.se/~larsg/Site/download.html 
, scroll down to "Astromodels" to get all of the Excel spreadsheets if you want 
to try them out. He has Ptolemy Almagest, two Arab astronomers, Toledan, and 
Alfsono.

Thanks for your interest. I'll share my final result with you before daring to 
publish it. I would be interested to know more about the methods of astrologers 
in the 14th-15th centuries in Milan, including astrolabes, which is John Davis' 
specialty.

Best regards,

Ross Caldwell
43.349399 3.22422981
Béziers, France

De : Schechner, Sara 
Envoyé : mardi 30 juin 2020 22:20
À : Ross Sinclair Caldwell 
Cc : 'sundial list sundials' 
Objet : 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

RE: Time problem

2020-06-30 Thread Schechner, Sara

>>> 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  | @SaraSchechner
http://scholar.harvard.edu/saraschechner
http://chsi.harvard.edu/



---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Re: Time problem

2020-06-30 Thread Michael Ossipoff

According to a graph from Lascar, in 1986, the greater obliquity of the
elcliptic 700 years ago would, even at the Winter-Solstice, only change
Sunrise-time (in local true Solar time) at lat 46 by about half a minute.

In fact, even with the greatest obliquity that ever occurs in the current
cycle, that lat 46 Winter-Solstice Sunrise time would only differ from now
by about 6 minutes.

So evidently one of your sources has simply made a big error of some kind.

On Tue, Jun 30, 2020 at 10:06 AM Ross Sinclair Caldwell <
belmu...@hotmail.com> wrote:

> Hi Jack,
>
> Thanks for thinking about this problem.
>
> It isn't the clock time, in any system, that matters here. The biographer
> - Pier Candido Decembrio - reports only that it was six minutes after
> sunrise. So all that matters is to determine when sunrise was, by any
> system we can, in order to be able to put the data into an astronomy
> program or a helpful spreadsheet using medieval values, like Lars Gislén's
> "Astromodels" for the Alfonsine Tables, which those astrologers probably
> used. http://home.thep.lu.se/~larsg/Site/download.html
>
> The problem I encounter is that two very apparently reliable sources give
> different times for the sunrise from Milan on that day, once the date is
> corrected to Gregorian and given a Julian day.
>
> The NOAA site gives 06:22 CET, the program Stellarium gives 06:00. On
> Stellarium, today I went back year by year, and noticed that they not only
> automatically switch to Julian calendar before 15 October 1582, but also
> make a change in  times in the year 1847. In both Béziers, where I live,
> and Milan, sunrise for 1 October is 07:22 (what is the historical basis for
> this additional hour?) in 1848, but goes to 06:00 in 1847 and all the years
> thence back to 1583 (within a minute or so, for the quarter days leading to
> a leap year). In 1582, 1 October sunrise in Milan is 06:12, so you have to
> know to change to the Julian calendar date of 23 September to get the right
> sunrise, which is 06:01.
>
> Hank showed from the "old" NOAA Earth System Research Lab page
> https://www.esrl.noaa.gov/gmd/grad/solcalc/sunrise.html that putting in
> the data with the UTC offset at +0.61 for Milan (-0.61 for American users)
> at that longitude produced the "correct" time at 05:58, so with a few more
> decimals it would be within a minute of the Stellarium and YourSky programs
> (which rigorously uses Meeus, I believe).
>
> I am leaning to a 06:00 as the consensus.
>
> Ross
>
>
> --
> *De :* Jack Aubert 
> *Envoyé :* mardi 30 juin 2020 15:31
> *À :* 'Ross Sinclair Caldwell' ; 'Michael Ossipoff'
> 
> *Cc :* 'sundial list sundials' 
> *Objet :* RE: Time problem
>
>
> I have been thinking about this problem but I may not be understanding it
> correctly.  I think you want to find out what time sunrise was on September
> 23 in 1392.  Because of the change from Julian to Gregorian dates, this
> corresponds to our October 1.  On October 1, a real clock in Milan this
> year would not tell quite the same time as a municipal clock in 1392,
> though.
>
>
>
> We can easily correct for daylight saving time.  The second thing to
> consider would be the equation of time.  But it has changed very little
> between 1329 and now, so sunrise on October 1 1329 in Milan should be
> almost the same time as it is now, so if you could transport a modern clock
> to Milan in 1329, it would show sunrise at very close to the same time as
> it does now.  But this would not necessarily be the case in 1392.  At that
> time, clocks would normally not take the equation of time into account at
> all.  Since they were not very accurate over an extended period, they would
> have had to be adjusted frequently using a sundial.  So the municipal clock
> would probably have shown noon at what we would call 12:11.  It is possible
> that a clock used by an astronomer might make the adjustment using a
> contemporaneous equation of time table (which would have been less accurate
> than our calculation) but this seems unlikely.
>
>
>
> The other thing to take into account is Milan's longitude.  At 9.11
> degrees East, Milan is six degrees from the 15 degree time zone center, for
> a clock offset of 24 minutes.   So a calculation for modern civil time at
> that location should include both the longitude and equation of time.  A
> calculation of contemporary civil time would obviously not have included a
> time zone offset, I think, should not have included the equation of time
> either.
>
>
>
> It sounds to me as if the programs may be handling the longitude offset,
> and possibly the equation of time differently.
>
>
>
> Does this make sense

RE: Time problem

2020-06-30 Thread Ross Sinclair Caldwell

Hi Jack,

Thanks for thinking about this problem.

It isn't the clock time, in any system, that matters here. The biographer - 
Pier Candido Decembrio - reports only that it was six minutes after sunrise. So 
all that matters is to determine when sunrise was, by any system we can, in 
order to be able to put the data into an astronomy program or a helpful 
spreadsheet using medieval values, like Lars Gislén's "Astromodels" for the 
Alfonsine Tables, which those astrologers probably used. 
http://home.thep.lu.se/~larsg/Site/download.html

The problem I encounter is that two very apparently reliable sources give 
different times for the sunrise from Milan on that day, once the date is 
corrected to Gregorian and given a Julian day.

The NOAA site gives 06:22 CET, the program Stellarium gives 06:00. On 
Stellarium, today I went back year by year, and noticed that they not only 
automatically switch to Julian calendar before 15 October 1582, but also make a 
change in  times in the year 1847. In both Béziers, where I live, and Milan, 
sunrise for 1 October is 07:22 (what is the historical basis for this 
additional hour?) in 1848, but goes to 06:00 in 1847 and all the years thence 
back to 1583 (within a minute or so, for the quarter days leading to a leap 
year). In 1582, 1 October sunrise in Milan is 06:12, so you have to know to 
change to the Julian calendar date of 23 September to get the right sunrise, 
which is 06:01.

Hank showed from the "old" NOAA Earth System Research Lab page 
https://www.esrl.noaa.gov/gmd/grad/solcalc/sunrise.html that putting in the 
data with the UTC offset at +0.61 for Milan (-0.61 for American users) at that 
longitude produced the "correct" time at 05:58, so with a few more decimals it 
would be within a minute of the Stellarium and YourSky programs (which 
rigorously uses Meeus, I believe).

I am leaning to a 06:00 as the consensus.

Ross



De : Jack Aubert 
Envoyé : mardi 30 juin 2020 15:31
À : 'Ross Sinclair Caldwell' ; 'Michael Ossipoff' 

Cc : 'sundial list sundials' 
Objet : RE: Time problem


I have been thinking about this problem but I may not be understanding it 
correctly.  I think you want to find out what time sunrise was on September 23 
in 1392.  Because of the change from Julian to Gregorian dates, this 
corresponds to our October 1.  On October 1, a real clock in Milan this year 
would not tell quite the same time as a municipal clock in 1392, though.



We can easily correct for daylight saving time.  The second thing to consider 
would be the equation of time.  But it has changed very little between 1329 and 
now, so sunrise on October 1 1329 in Milan should be almost the same time as it 
is now, so if you could transport a modern clock to Milan in 1329, it would 
show sunrise at very close to the same time as it does now.  But this would not 
necessarily be the case in 1392.  At that time, clocks would normally not take 
the equation of time into account at all.  Since they were not very accurate 
over an extended period, they would have had to be adjusted frequently using a 
sundial.  So the municipal clock would probably have shown noon at what we 
would call 12:11.  It is possible that a clock used by an astronomer might make 
the adjustment using a contemporaneous equation of time table (which would have 
been less accurate than our calculation) but this seems unlikely.



The other thing to take into account is Milan's longitude.  At 9.11 degrees 
East, Milan is six degrees from the 15 degree time zone center, for a clock 
offset of 24 minutes.   So a calculation for modern civil time at that location 
should include both the longitude and equation of time.  A calculation of 
contemporary civil time would obviously not have included a time zone offset, I 
think, should not have included the equation of time either.



It sounds to me as if the programs may be handling the longitude offset, and 
possibly the equation of time differently.



Does this make sense?



Jack Aubert



From: sundial  On Behalf Of Ross Sinclair Caldwell
Sent: Monday, June 29, 2020 2:06 PM
To: Michael Ossipoff 
Cc: sundial list sundials 
Subject: RE: Time problem



Yes, but I don't know if any estimation of refraction or diameter would account 
for 20 minutes!



In any case, the real time is scarcely relevant - they only wanted to say that 
it was shortly after sunrise, sufficiently so that the Sun  was estimated to be 
clear of the horizon.



The clock they used only matters for the calculation of minutes, which with a 
24-hour clock, however calibrated, would be the same as ours for all practical 
purposes.



The biographer doesn't give the time in clock time, only minutes after sunrise. 
This is why I want to know what that is. The true time of his birth is 
absolutely irrelevant; we only need to know what they believed, and interpreted 
from that belief.



Ross



De : Mic

RE: Time problem

2020-06-30 Thread Jack Aubert

I have been thinking about this problem but I may not be understanding it
correctly.  I think you want to find out what time sunrise was on September
23 in 1392.  Because of the change from Julian to Gregorian dates, this
corresponds to our October 1.  On October 1, a real clock in Milan this year
would not tell quite the same time as a municipal clock in 1392, though.  

 

We can easily correct for daylight saving time.  The second thing to
consider would be the equation of time.  But it has changed very little
between 1329 and now, so sunrise on October 1 1329 in Milan should be almost
the same time as it is now, so if you could transport a modern clock to
Milan in 1329, it would show sunrise at very close to the same time as it
does now.  But this would not necessarily be the case in 1392.  At that
time, clocks would normally not take the equation of time into account at
all.  Since they were not very accurate over an extended period, they would
have had to be adjusted frequently using a sundial.  So the municipal clock
would probably have shown noon at what we would call 12:11.  It is possible
that a clock used by an astronomer might make the adjustment using a
contemporaneous equation of time table (which would have been less accurate
than our calculation) but this seems unlikely.  

 

The other thing to take into account is Milan's longitude.  At 9.11 degrees
East, Milan is six degrees from the 15 degree time zone center, for a clock
offset of 24 minutes.   So a calculation for modern civil time at that
location should include both the longitude and equation of time.  A
calculation of contemporary civil time would obviously not have included a
time zone offset, I think, should not have included the equation of time
either. 

 

It sounds to me as if the programs may be handling the longitude offset, and
possibly the equation of time differently.   

 

Does this make sense?  

 

Jack Aubert  

 

From: sundial  On Behalf Of Ross Sinclair
Caldwell
Sent: Monday, June 29, 2020 2:06 PM
To: Michael Ossipoff 
Cc: sundial list sundials 
Subject: RE: Time problem

 

Yes, but I don't know if any estimation of refraction or diameter would
account for 20 minutes!

 

In any case, the real time is scarcely relevant - they only wanted to say
that it was shortly after sunrise, sufficiently so that the Sun  was
estimated to be clear of the horizon. 

 

The clock they used only matters for the calculation of minutes, which with
a 24-hour clock, however calibrated, would be the same as ours for all
practical purposes.

 

The biographer doesn't give the time in clock time, only minutes after
sunrise. This is why I want to know what that is. The true time of his birth
is absolutely irrelevant; we only need to know what they believed, and
interpreted from that belief. 

 

Ross

  _  

De : Michael Ossipoff mailto:email9648...@gmail.com> >
Envoyé : lundi 29 juin 2020 19:31
À : Ross Sinclair Caldwell mailto:belmu...@hotmail.com> >
Cc : sundial list sundials mailto:sundial@uni-koeln.de> >
Objet : Re: Time problem 

 

Okay, but there's the inaccuracy of the clocks in those days, and the
importance of that would depend on how they determined Sunrise. I guess they
set the clocks by sundial or noon-mark, but, as you said, it depends on how
often they set them.

 

Anyway, the difference between the NOAA Sunrise-time, and the one calculated
by the planetarium-programs could result from the planetarium-programs not
taking into account the changes in orbit or obliquity.  I'd expect that the
NOAA figure would be more reliable.

 

Sunrise & Sunset times are usually calculated using a standard value for
atmospheric refraction at the horizon. The usual assumption is that the
refraction is 34 minutes and that the Sun's apparent semi-diameter is 16
minutes. Maybe NOAA used a calculated semi-diameter instead of the standard
16 minutes.

 

You don't have sufficiently reliably accurate information for a horoscope
accurate to the minute, and another reason for that is that unusual
atmospheric refractivity could change Sunrise-time by minutes.

 

Michael

 

 

 

On Mon, Jun 29, 2020 at 1:09 PM Ross Sinclair Caldwell mailto:belmu...@hotmail.com> > wrote:

 

Hi Michael,

 

Also, when they said that he was born a certain number of minutes after
Sunrise, how did they determine that? By judging when it seemed to be
Sunrise, when the Sun appeared over the trees, mountains or buildings, or by
calculating Sunrise-time based on a 14th century estimate of Milan's
longiitude?  And were they minutes of equal-hours time, or of
temporary-hours time?

I can answer some of those questions with reasonable certainty. 

 

For minutes, they used an equal-hour 24 hour clock, beginning a half-hour
after sunset the previous day. That is, the clock would strike "1" at, say,
at our 20:45 on that particular day (30 September Gregorian). Of course it
was constantly adjusted, with what frequen

RE: Time problem

2020-06-29 Thread Ross Sinclair Caldwell

Yes, but I don't know if any estimation of refraction or diameter would account 
for 20 minutes!

In any case, the real time is scarcely relevant - they only wanted to say that 
it was shortly after sunrise, sufficiently so that the Sun  was estimated to be 
clear of the horizon.

The clock they used only matters for the calculation of minutes, which with a 
24-hour clock, however calibrated, would be the same as ours for all practical 
purposes.

The biographer doesn't give the time in clock time, only minutes after sunrise. 
This is why I want to know what that is. The true time of his birth is 
absolutely irrelevant; we only need to know what they believed, and interpreted 
from that belief.

Ross

De : Michael Ossipoff 
Envoyé : lundi 29 juin 2020 19:31
À : Ross Sinclair Caldwell 
Cc : sundial list sundials 
Objet : Re: Time problem

Okay, but there's the inaccuracy of the clocks in those days, and the 
importance of that would depend on how they determined Sunrise. I guess they 
set the clocks by sundial or noon-mark, but, as you said, it depends on how 
often they set them.

Anyway, the difference between the NOAA Sunrise-time, and the one calculated by 
the planetarium-programs could result from the planetarium-programs not taking 
into account the changes in orbit or obliquity.  I'd expect that the NOAA 
figure would be more reliable.

Sunrise & Sunset times are usually calculated using a standard value for 
atmospheric refraction at the horizon. The usual assumption is that the 
refraction is 34 minutes and that the Sun's apparent semi-diameter is 16 
minutes. Maybe NOAA used a calculated semi-diameter instead of the standard 16 
minutes.

You don't have sufficiently reliably accurate information for a horoscope 
accurate to the minute, and another reason for that is that unusual atmospheric 
refractivity could change Sunrise-time by minutes.

Michael



On Mon, Jun 29, 2020 at 1:09 PM Ross Sinclair Caldwell 
mailto:belmu...@hotmail.com>> wrote:

Hi Michael,

Also, when they said that he was born a certain number of minutes after 
Sunrise, how did they determine that? By judging when it seemed to be Sunrise, 
when the Sun appeared over the trees, mountains or buildings, or by calculating 
Sunrise-time based on a 14th century estimate of Milan's longiitude?  And were 
they minutes of equal-hours time, or of temporary-hours time?
I can answer some of those questions with reasonable certainty.

For minutes, they used an equal-hour 24 hour clock, beginning a half-hour after 
sunset the previous day. That is, the clock would strike "1" at, say, at our 
20:45 on that particular day (30 September Gregorian). Of course it was 
constantly adjusted, with what frequency I don't know. Obviously it depended on 
the season, but there must have also been a regular schedule of maintenance for 
the mechanism. I don't know if an example of such a schedule survives from any 
of these early clocks, since Europe generally moved to the equal-hour 24-hour 
day starting at midnight in the sixteenth century.

For sunrise, it is a flat view east of Milan, and the part of the castle where 
he is reported to have been born was one of the highest places in the city. 
From the top of one of the four corner towers, you would see clear to the 
eastern horizon. But it is possible they made a calculation rather than an 
observation, and so perhaps it was theoretical rather than observed, even if 
they used an hourglass with minutes we would recognize. Even if it were a 
cloudy morning, they knew what time the sun rose.

For what value it had, the propaganda, since he was the second son, he was not 
expected to inherit the throne, so there was less reason to fudge the data to 
make him appear better than he was. The day of birth was a public announcement; 
the time was apparently a closely guarded secret, since astrology could be a 
political weapon.

Ross

De : Michael Ossipoff mailto:email9648...@gmail.com>>
Envoyé : lundi 29 juin 2020 18:39
À : Ross Sinclair Caldwell mailto:belmu...@hotmail.com>>
Cc : sundial list sundials mailto:sundial@uni-koeln.de>>
Objet : Re: Time problem

Of course, even if the Earth's orbit didn't change, no civil calendar keeps a 
constant relation between date and ecliptic-longitude.  So you'd have to 
determine the calendar's date-ecliptic-longitude displacement for the date of 
interest.
.
But the Earth's orbit does change. Our orbit's eccentricity, and the relation 
between the apsides and the equinoxes have been steadily changing since the 
14th century. ...as has the obliquity of the ecliptic.
.
Might some of the commercially-available planetarium-programs disregard that? 
Sure. At least some of those programs ignore changes in the precessional-rate, 
so why expect them to take into account the changing eccentricity, 
apsides/equinoxes relation, and obliquity of the ecliptic?
.
Also, when they

Re: Time problem

2020-06-29 Thread Michael Ossipoff

Okay, but there's the inaccuracy of the clocks in those days, and the
importance of that would depend on how they determined Sunrise. I guess
they set the clocks by sundial or noon-mark, but, as you said, it depends
on how often they set them.

Anyway, the difference between the NOAA Sunrise-time, and the one
calculated by the planetarium-programs could result from the
planetarium-programs not taking into account the changes in orbit or
obliquity.  I'd expect that the NOAA figure would be more reliable.

Sunrise & Sunset times are usually calculated using a standard value for
atmospheric refraction at the horizon. The usual assumption is that the
refraction is 34 minutes and that the Sun's apparent semi-diameter is 16
minutes. Maybe NOAA used a calculated semi-diameter instead of the standard
16 minutes.

You don't have sufficiently reliably accurate information for a horoscope
accurate to the minute, and another reason for that is that unusual
atmospheric refractivity could change Sunrise-time by minutes.

Michael



On Mon, Jun 29, 2020 at 1:09 PM Ross Sinclair Caldwell 
wrote:

>
> Hi Michael,
>
> Also, when they said that he was born a certain number of minutes after
> Sunrise, how did they determine that? By judging when it seemed to be
> Sunrise, when the Sun appeared over the trees, mountains or buildings, or
> by calculating Sunrise-time based on a 14th century estimate of Milan's
> longiitude?  And were they minutes of equal-hours time, or of
> temporary-hours time?
>
> I can answer some of those questions with reasonable certainty.
>
> For minutes, they used an equal-hour 24 hour clock, beginning a half-hour
> after sunset the previous day. That is, the clock would strike "1" at, say,
> at our 20:45 on that particular day (30 September Gregorian). Of course it
> was constantly adjusted, with what frequency I don't know. Obviously it
> depended on the season, but there must have also been a regular schedule of
> maintenance for the mechanism. I don't know if an example of such a
> schedule survives from any of these early clocks, since Europe generally
> moved to the equal-hour 24-hour day starting at midnight in the sixteenth
> century.
>
> For sunrise, it is a flat view east of Milan, and the part of the castle
> where he is reported to have been born was one of the highest places in the
> city. From the top of one of the four corner towers, you would see clear to
> the eastern horizon. But it is possible they made a calculation rather than
> an observation, and so perhaps it was theoretical rather than observed,
> even if they used an hourglass with minutes we would recognize. Even if it
> were a cloudy morning, they knew what time the sun rose.
>
> For what value it had, the propaganda, since he was the second son, he was
> not expected to inherit the throne, so there was less reason to fudge the
> data to make him appear better than he was. The day of birth was a public
> announcement; the time was apparently a closely guarded secret, since
> astrology could be a political weapon.
>
> Ross
> --
> *De :* Michael Ossipoff 
> *Envoyé :* lundi 29 juin 2020 18:39
> *À :* Ross Sinclair Caldwell 
> *Cc :* sundial list sundials 
> *Objet :* Re: Time problem
>
> Of course, even if the Earth's orbit didn't change, no civil calendar
> keeps a constant relation between date and ecliptic-longitude.  So you'd
> have to determine the calendar's date-ecliptic-longitude displacement for
> the date of interest.
> .
> But the Earth's orbit does change. Our orbit's eccentricity, and the
> relation between the apsides and the equinoxes have been steadily changing
> since the 14th century. ...as has the obliquity of the ecliptic.
> .
> Might some of the commercially-available planetarium-programs disregard
> that? Sure. At least some of those programs ignore changes in the
> precessional-rate, so why expect them to take into account the changing
> eccentricity, apsides/equinoxes relation, and obliquity of the ecliptic?
> .
> Also, when they said that he was born a certain number of minutes after
> Sunrise, how did they determine that? By judging when it seemed to be
> Sunrise, when the Sun appeared over the trees, mountains or buildings, or
> by calculating Sunrise-time based on a 14th century estimate of Milan's
> longiitude?  And were they minutes of equal-hours time, or of
> temporary-hours time?
> .
> Michael Ossipoff
>
>
>
>
>
> On Mon, Jun 29, 2020 at 5:23 AM Ross Sinclair Caldwell <
> belmu...@hotmail.com> wrote:
>
> Hi diallists,
>
> This is not a sundial problem, but a time discrepancy I don't understand
> between NOAA sunrise calculations and the results of two reliable
> planetarium programs, Stellarium and YourSky (part

RE: Time problem

2020-06-29 Thread Ross Sinclair Caldwell


Hi Michael,

Also, when they said that he was born a certain number of minutes after 
Sunrise, how did they determine that? By judging when it seemed to be Sunrise, 
when the Sun appeared over the trees, mountains or buildings, or by calculating 
Sunrise-time based on a 14th century estimate of Milan's longiitude?  And were 
they minutes of equal-hours time, or of temporary-hours time?
I can answer some of those questions with reasonable certainty.

For minutes, they used an equal-hour 24 hour clock, beginning a half-hour after 
sunset the previous day. That is, the clock would strike "1" at, say, at our 
20:45 on that particular day (30 September Gregorian). Of course it was 
constantly adjusted, with what frequency I don't know. Obviously it depended on 
the season, but there must have also been a regular schedule of maintenance for 
the mechanism. I don't know if an example of such a schedule survives from any 
of these early clocks, since Europe generally moved to the equal-hour 24-hour 
day starting at midnight in the sixteenth century.

For sunrise, it is a flat view east of Milan, and the part of the castle where 
he is reported to have been born was one of the highest places in the city. 
From the top of one of the four corner towers, you would see clear to the 
eastern horizon. But it is possible they made a calculation rather than an 
observation, and so perhaps it was theoretical rather than observed, even if 
they used an hourglass with minutes we would recognize. Even if it were a 
cloudy morning, they knew what time the sun rose.

For what value it had, the propaganda, since he was the second son, he was not 
expected to inherit the throne, so there was less reason to fudge the data to 
make him appear better than he was. The day of birth was a public announcement; 
the time was apparently a closely guarded secret, since astrology could be a 
political weapon.

Ross

De : Michael Ossipoff 
Envoyé : lundi 29 juin 2020 18:39
À : Ross Sinclair Caldwell 
Cc : sundial list sundials 
Objet : Re: Time problem

Of course, even if the Earth's orbit didn't change, no civil calendar keeps a 
constant relation between date and ecliptic-longitude.  So you'd have to 
determine the calendar's date-ecliptic-longitude displacement for the date of 
interest.
.
But the Earth's orbit does change. Our orbit's eccentricity, and the relation 
between the apsides and the equinoxes have been steadily changing since the 
14th century. ...as has the obliquity of the ecliptic.
.
Might some of the commercially-available planetarium-programs disregard that? 
Sure. At least some of those programs ignore changes in the precessional-rate, 
so why expect them to take into account the changing eccentricity, 
apsides/equinoxes relation, and obliquity of the ecliptic?
.
Also, when they said that he was born a certain number of minutes after 
Sunrise, how did they determine that? By judging when it seemed to be Sunrise, 
when the Sun appeared over the trees, mountains or buildings, or by calculating 
Sunrise-time based on a 14th century estimate of Milan's longiitude?  And were 
they minutes of equal-hours time, or of temporary-hours time?
.
Michael Ossipoff





On Mon, Jun 29, 2020 at 5:23 AM Ross Sinclair Caldwell 
mailto:belmu...@hotmail.com>> wrote:
Hi diallists,

This is not a sundial problem, but a time discrepancy I don't understand 
between NOAA sunrise calculations and the results of two reliable planetarium 
programs, Stellarium and YourSky (part of HomePlanet). http://stellarium.org/  
https://www.fourmilab.ch/yoursky/ https://www.fourmilab.ch/homeplanet/

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.

First step - get the Gregorian equivalent, and the Julian day. This is 1 
October 1392 Gregorian, which is Julian day 2229751.5 (".5" because Julian days 
start on noon, and the .5 represents midnight, the beginning of 23 September 
Julian/1 October Gregorian).

Now, both Stellarium and YourSky automatically correct for the change from 
Julian calendar to Gregorian. That is, if you look at the sky for 15 October 
1582, and then go back one day, the calendar reads 4 October 1582. This was the 
change mandated by Pope Gregory, that Thursday 4 October 1582 would be followed 
Friday 15 October 1582.

So, there is no need to use 1 October 1392 for my purposes - both programs read 
23 September as Julian day 2229751.5(etc).

These programs give the sunrise in Milan on that date at 06:00 and 05:59 
respectively. Obviously they use an ideal horizon, but t

Re: Time problem

2020-06-29 Thread Michael Ossipoff

Of course, even if the Earth's orbit didn't change, no civil calendar keeps
a constant relation between date and ecliptic-longitude.  So you'd have to
determine the calendar's date-ecliptic-longitude displacement for the date
of interest.
.
But the Earth's orbit does change. Our orbit's eccentricity, and the
relation between the apsides and the equinoxes have been steadily changing
since the 14th century. ...as has the obliquity of the ecliptic.
.
Might some of the commercially-available planetarium-programs disregard
that? Sure. At least some of those programs ignore changes in the
precessional-rate, so why expect them to take into account the changing
eccentricity, apsides/equinoxes relation, and obliquity of the ecliptic?
.
Also, when they said that he was born a certain number of minutes after
Sunrise, how did they determine that? By judging when it seemed to be
Sunrise, when the Sun appeared over the trees, mountains or buildings, or
by calculating Sunrise-time based on a 14th century estimate of Milan's
longiitude?  And were they minutes of equal-hours time, or of
temporary-hours time?
.
Michael Ossipoff





On Mon, Jun 29, 2020 at 5:23 AM Ross Sinclair Caldwell 
wrote:

> Hi diallists,
>
> This is not a sundial problem, but a time discrepancy I don't understand
> between NOAA sunrise calculations and the results of two reliable
> planetarium programs, Stellarium and YourSky (part of HomePlanet).
> http://stellarium.org/  https://www.fourmilab.ch/yoursky/
> https://www.fourmilab.ch/homeplanet/
>
> 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.
>
> First step - get the Gregorian equivalent, and the Julian day. This is 1
> October 1392 Gregorian, which is Julian day 2229751.5 (".5" because Julian
> days start on noon, and the .5 represents midnight, the beginning of 23
> September Julian/1 October Gregorian).
>
> Now, both Stellarium and YourSky automatically correct for the change from
> Julian calendar to Gregorian. That is, if you look at the sky for 15
> October 1582, and then go back one day, the calendar reads 4 October 1582.
> This was the change mandated by Pope Gregory, that Thursday 4 October 1582
> would be followed Friday 15 October 1582.
>
> So, there is no need to use 1 October 1392 for my purposes - both programs
> read 23 September as Julian day 2229751.5(etc).
>
> These programs give the sunrise in Milan on that date at 06:00 and 05:59
> respectively. Obviously they use an ideal horizon, but the view east from
> Milan is flat, so there is nothing delaying the appearance of the sun.
>
> Now,, when you go to NOAA's Solar Calculator, they use straight Gregorian
> dates. That is, you can get sunrise times for 5, 6, 7, etc. up to 14
> October, 1582. So you have to use the Gregorian equivalent of 23 September
> 1392, which is 1 October. https://www.esrl.noaa.gov/gmd/grad/solcalc/
>
> They give the sunrise time as 06:22 on 1 October 1392. If you are in doubt
> about the Gregorian/Julian switch, they give the time on 23 September as
> 06:12. Neither is in agreement, in any case, with the astronomy programs.
>
> Now, the difference between 1392 and today should be negligible in any
> case. We can just as well use this year's 1 October for the time of
> sunrise. Of course, it is 06:22 (or 07:22 since in 2020 Italy uses daylight
> saving time).
>
> In order to get a sunrise time of 06:22 on Stellarium, I have to push the
> date to 11 October.
>
> The problem is that both NOAA and the astronomy programs are right for me
> for sunrise and sunset in Béziers today (within a minute).
>
> So, the astronomy programs are apparently wrong for the 1392 date. This is
> not really ancient, so I wonder if anyone could suggest to me why it might
> be that there is 22 minutes' difference between these programs and the NOAA
> data for the same date?
>
> Thank you for any thoughts that anyone might have.
>
> Ross Caldwell
> 43.349399 3.22422981
> Béziers
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
>
---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Re: Time problem

2020-06-29 Thread Hank de Wit


Hi Ross,


Are you making Time Zone adjustments?. When I start Stellarium, by 
default it uses my own time zone even if I change location. I have to go 
to the Plugins and explicitly set a time zone. I imagine you should be 
working in the local time of Milan, which I estimated roughly at (9.2 
deg E) or +37 minutes ahead of Greenwich. I can't explain 22 minutes 
with this thought process though.



Cheers

Hank


On 29/6/20 6:46 pm, Ross Sinclair Caldwell wrote:

Hi diallists,

This is not a sundial problem, but a time discrepancy I don't 
understand between NOAA sunrise calculations and the results of two 
reliable planetarium programs, Stellarium and YourSky (part of 
HomePlanet). http://stellarium.org/ https://www.fourmilab.ch/yoursky/ 
https://www.fourmilab.ch/homeplanet/


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.


First step - get the Gregorian equivalent, and the Julian day. This is 
1 October 1392 Gregorian, which is Julian day 2229751.5 (".5" because 
Julian days start on noon, and the .5 represents midnight, the 
beginning of 23 September Julian/1 October Gregorian).


Now, both Stellarium and YourSky automatically correct for the change 
from Julian calendar to Gregorian. That is, if you look at the sky for 
15 October 1582, and then go back one day, the calendar reads 4 
October 1582. This was the change mandated by Pope Gregory, that 
Thursday 4 October 1582 would be followed Friday 15 October 1582.


So, there is no need to use 1 October 1392 for my purposes - both 
programs read 23 September as Julian day 2229751.5(etc).


These programs give the sunrise in Milan on that date at 06:00 and 
05:59 respectively. Obviously they use an ideal horizon, but the view 
east from Milan is flat, so there is nothing delaying the appearance 
of the sun.


Now,, when you go to NOAA's Solar Calculator, they use straight 
Gregorian dates. That is, you can get sunrise times for 5, 6, 7, etc. 
up to 14 October, 1582. So you have to use the Gregorian equivalent of 
23 September 1392, which is 1 October. 
https://www.esrl.noaa.gov/gmd/grad/solcalc/


They give the sunrise time as 06:22 on 1 October 1392. If you are in 
doubt about the Gregorian/Julian switch, they give the time on 23 
September as 06:12. Neither is in agreement, in any case, with the 
astronomy programs.


Now, the difference between 1392 and today should be negligible in any 
case. We can just as well use this year's 1 October for the time of 
sunrise. Of course, it is 06:22 (or 07:22 since in 2020 Italy uses 
daylight saving time).


In order to get a sunrise time of 06:22 on Stellarium, I have to push 
the date to 11 October.


The problem is that both NOAA and the astronomy programs are right for 
me for sunrise and sunset in Béziers today (within a minute).


So, the astronomy programs are apparently wrong for the 1392 date. 
This is not really ancient, so I wonder if anyone could suggest to me 
why it might be that there is 22 minutes' difference between these 
programs and the NOAA data for the same date?


Thank you for any thoughts that anyone might have.

Ross Caldwell
43.349399 3.22422981
Béziers

---
https://lists.uni-koeln.de/mailman/listinfo/sundial

---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Time problem

2020-06-29 Thread Ross Sinclair Caldwell

Hi diallists,

This is not a sundial problem, but a time discrepancy I don't understand 
between NOAA sunrise calculations and the results of two reliable planetarium 
programs, Stellarium and YourSky (part of HomePlanet). http://stellarium.org/  
https://www.fourmilab.ch/yoursky/ https://www.fourmilab.ch/homeplanet/

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.

First step - get the Gregorian equivalent, and the Julian day. This is 1 
October 1392 Gregorian, which is Julian day 2229751.5 (".5" because Julian days 
start on noon, and the .5 represents midnight, the beginning of 23 September 
Julian/1 October Gregorian).

Now, both Stellarium and YourSky automatically correct for the change from 
Julian calendar to Gregorian. That is, if you look at the sky for 15 October 
1582, and then go back one day, the calendar reads 4 October 1582. This was the 
change mandated by Pope Gregory, that Thursday 4 October 1582 would be followed 
Friday 15 October 1582.

So, there is no need to use 1 October 1392 for my purposes - both programs read 
23 September as Julian day 2229751.5(etc).

These programs give the sunrise in Milan on that date at 06:00 and 05:59 
respectively. Obviously they use an ideal horizon, but the view east from Milan 
is flat, so there is nothing delaying the appearance of the sun.

Now,, when you go to NOAA's Solar Calculator, they use straight Gregorian 
dates. That is, you can get sunrise times for 5, 6, 7, etc. up to 14 October, 
1582. So you have to use the Gregorian equivalent of 23 September 1392, which 
is 1 October. https://www.esrl.noaa.gov/gmd/grad/solcalc/

They give the sunrise time as 06:22 on 1 October 1392. If you are in doubt 
about the Gregorian/Julian switch, they give the time on 23 September as 06:12. 
Neither is in agreement, in any case, with the astronomy programs.

Now, the difference between 1392 and today should be negligible in any case. We 
can just as well use this year's 1 October for the time of sunrise. Of course, 
it is 06:22 (or 07:22 since in 2020 Italy uses daylight saving time).

In order to get a sunrise time of 06:22 on Stellarium, I have to push the date 
to 11 October.

The problem is that both NOAA and the astronomy programs are right for me for 
sunrise and sunset in Béziers today (within a minute).

So, the astronomy programs are apparently wrong for the 1392 date. This is not 
really ancient, so I wonder if anyone could suggest to me why it might be that 
there is 22 minutes' difference between these programs and the NOAA data for 
the same date?

Thank you for any thoughts that anyone might have.

Ross Caldwell
43.349399 3.22422981
Béziers
---
https://lists.uni-koeln.de/mailman/listinfo/sundial

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