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• Calculating the start and stop of daylight requires knowing the day of the week This is similar to determining Easter. Pastor Zellar in 1886 developed a
Message 1 of 10 , Feb 6, 2006
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Calculating the start and stop of daylight requires knowing the day of the week

This is similar to determining Easter.

Pastor Zellar in 1886 developed a formula for calculating the day of the week for any Gregorian date. Zeller's Congruence (or Algorithm) gives Day-of-Week from Calendar Date. Methods, which are also used to calculate Day-Count.

I optimized it for computers.

Professor Dr J R Stockton, Surrey, UK. optimized it also and his runs twice as fast as what I had developed.

The following information is from Stockton’s web site.

Zeller (1822-99) a protestant minister in Markgröningen (Württemberg, SW Germany; 20 km NW of Stuttgart). The paper that describes how to determine the day of the week for Gregorian dates is  Kalender-Formeln, Acta Mathematica, 9:131-6, Nov 1886.  His goal was to determine the day of week necessary for determining Easter.

In addition to his Date papers, it appears that he published papers about number theory :-

·         “Ein neuer Beweis des Reziprozitäts-Theorems” (Berlin 1872)

·         “De numeris Bernoulli eorumque compositione ex numeris integris et reciprocis primis” (Paris 1881)

·         “Zu Eulers Recursionsformel für die Divisorensummen” (Stockholm 1884)

In 1882 he was admitted into the Société Mathématique de France. His later honours included the Order of Friedrich, First Class, and the Ritterkreuz of Württemberg. He retired in 1898, and died in the following Summer. In 1874, he became Director of the Seminary in Markgröningen, together with the girls’ orphanage there. He was married twice, having 9 children and 36 grandchildren.

I am impressed with the man.

hjw

• Calculating the start and stop of daylight requires knowing the day of the week Why do you say this? I suspect if you know the latitude and longitude and
Message 2 of 10 , Feb 6, 2006
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"Calculating the start and stop of daylight requires knowing the day of the week"

Why do you say this?

I suspect if you know the latitude and longitude and some indicators of the duration since the longest and/or shortest day of the year, you can predict the times.

My point is only that although there may be algorithms based on day of the week, surely it is not the only way to calculate sunrise and sunset.

Tex Texin
Internationalization Architect,   Yahoo! Inc.

-----Original Message-----

Calculating the start and stop of daylight requires knowing the day of the week

This is similar to determining Easter.

Pastor Zellar in 1886 developed a formula for calculating the day of the week for any Gregorian date. Zeller's Congruence (or Algorithm) gives Day-of-Week from Calendar Date. Methods, which are also used to calculate Day-Count.

I optimized it for computers.

Professor Dr J R Stockton, Surrey, UK. optimized it also and his runs twice as fast as what I had developed.

The following information is from Stockton’s web site.

Zeller (1822-99) a protestant minister in Markgröningen (Württemberg, SW Germany; 20 km NW of Stuttgart). The paper that describes how to determine the day of the week for Gregorian dates is  Kalender-Formeln, Acta Mathematica, 9:131-6, Nov 1886.  His goal was to determine the day of week necessary for determining Easter.

In addition to his Date papers, it appears that he published papers about number theory :-

·         “Ein neuer Beweis des Reziprozitäts-Theorems” (Berlin 1872)

·         “De numeris Bernoulli eorumque compositione ex numeris integris et reciprocis primis” (Paris 1881)

·         “Zu Eulers Recursionsformel für die Divisorensummen” (Stockholm 1884)

In 1882 he was admitted into the Société Mathématique de France. His later honours included the Order of Friedrich, First Class, and the Ritterkreuz of Württemberg. He retired in 1898, and died in the following Summer. In 1874, he became Director of the Seminary in Markgröningen, together with the girls’ orphanage there. He was married twice, having 9 children and 36 grandchildren.

I am impressed with the man.

hjw

• In a message dated 2/7/2006 2:25:35 A.M. Central Daylight Time, tex@yahoo-inc.com writes: Calculating the start and stop of daylight requires knowing the day
Message 3 of 10 , Feb 7, 2006
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In a message dated 2/7/2006 2:25:35 A.M. Central Daylight Time, tex@... writes:

"Calculating the start and stop of daylight requires knowing the day of the week"

Why do you say this?

I suspect if you know the latitude and longitude and some indicators of the duration since the longest and/or shortest day of the year, you can predict the times.
I disagree.  i have done it.  Have you?

My point is only that although there may be algorithms based on day of the week, surely it is not the only way to calculate sunrise and sunset.

Tex Texin
Internationalization Architect,   Yahoo! Inc.
hjw
• Yes a long long time ago. So explain to me why the day of the week matters. Or to put it another way, why does 1/4 of a lunar cycle have any bearing on solar
Message 4 of 10 , Feb 7, 2006
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Yes a long long time ago.
So explain to me why the day of the week matters. Or to put it another way, why does 1/4 of a lunar cycle have any bearing on solar events.

Tex Texin
Internationalization Architect,   Yahoo! Inc.

-----Original Message-----
From: ISO8601@yahoogroups.com [mailto:ISO8601@yahoogroups.com] On Behalf Of hjwoudenberg@...
Sent: Tuesday, February 07, 2006 12:36 AM
To: ISO8601@yahoogroups.com
Subject: Re: [ISO8601] My kids found the following interesting, maybe you might also.

In a message dated 2/7/2006 2:25:35 A.M. Central Daylight Time, tex@... writes:

"Calculating the start and stop of daylight requires knowing the day of the week"

Why do you say this?

I suspect if you know the latitude and longitude and some indicators of the duration since the longest and/or shortest day of the year, you can predict the times.
I disagree.  i have done it.  Have you?

My point is only that although there may be algorithms based on day of the week, surely it is not the only way to calculate sunrise and sunset.

Tex Texin
Internationalization Architect,   Yahoo! Inc.
hjw
• In a message dated 2/7/2006 3:55:53 A.M. Central Daylight Time, tex@yahoo-inc.com writes: So explain to me why the day of the week matters. Or to put it
Message 5 of 10 , Feb 7, 2006
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In a message dated 2/7/2006 3:55:53 A.M. Central Daylight Time, tex@... writes:
So explain to me why the day of the week matters. Or to put it another way, why does 1/4 of a lunar cycle have any bearing on solar events.

Daylight starts on Sundays in western cultures.
Therefore for this year I must know what date is Sunday, sometime for the first of the month or last of the month, or after the 15th of the month.
Where is the problem?

hjw
• The problem is terminology. I am guessing you mean the date when Daylight Saving time starts and stops. I thought you were talking about daylight - ie the
Message 6 of 10 , Feb 7, 2006
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The problem is terminology. I am guessing you mean the date when Daylight Saving time starts and stops.
I thought you were talking about "daylight"- ie the time the sunrises and the time the sunsets on any day.

Tex Texin
Internationalization Architect,   Yahoo! Inc.

-----Original Message-----
From: ISO8601@yahoogroups.com [mailto:ISO8601@yahoogroups.com] On Behalf Of hjwoudenberg@...
Sent: Tuesday, February 07, 2006 1:17 AM
To: ISO8601@yahoogroups.com
Subject: Re: [ISO8601] My kids found the following interesting, maybe you might also.

In a message dated 2/7/2006 3:55:53 A.M. Central Daylight Time, tex@... writes:
So explain to me why the day of the week matters. Or to put it another way, why does 1/4 of a lunar cycle have any bearing on solar events.

Daylight starts on Sundays in western cultures.
Therefore for this year I must know what date is Sunday, sometime for the first of the month or last of the month, or after the 15th of the month.
Where is the problem?

hjw
• In a message dated 2/7/2006 3:55:53 A.M. Central Daylight Time, tex@yahoo-inc.com writes: So explain to me why the day of the week matters. Or to put it
Message 7 of 10 , Feb 7, 2006
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In a message dated 2/7/2006 3:55:53 A.M. Central Daylight Time, tex@... writes:
So explain to me why the day of the week matters. Or to put it another way, why does 1/4 of a lunar cycle have any bearing on solar events.

Tex Texin
Internationalization Architect,   Yahoo! Inc.
Time zones are legislative.  Therefore a day, like Sunday, occurs based on legislative decisions.

Sunday occurs because of legislative decisions of state or national government.

Therefore daylight is legislative, not for any other reason.

hjw
.

• In a message dated 2/7/2006 9:52:57 A.M. Central Daylight Time, tex@yahoo-inc.com writes: The problem is terminology. I am guessing you mean the date when
Message 8 of 10 , Feb 7, 2006
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In a message dated 2/7/2006 9:52:57 A.M. Central Daylight Time, tex@... writes:
The problem is terminology. I am guessing you mean the date when Daylight Saving time starts and stops.
I thought you were talking about "daylight"- ie the time the sunrises and the time the sunsets on any day.
yes, you are right.
I should have said daylight savings.

hjw

• ... runs ... I expect that the calculations built into the C library and such which yield day of week are similarly fast. I doubt I could beat them and would
Message 9 of 10 , Feb 7, 2006
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> I optimized it for computers.
> Professor Dr J R Stockton, Surrey, UK. optimized it also and his
runs
> twice as fast as what I had developed.

I expect that the calculations built into the C library and such which
yield day of week are similarly fast. I doubt I could beat them and
would not try.

<aside>
A month or so ago I was looking into finding the greatest common
divisor of two integers. I had a pretty crude algorithm that I had
written some years ago. After telling a colleague about it, he very
quickly pointed me in the right direction...

Euclid's algorithm, developed around 300 BC! Very very fast on a
computer.

http://aleph0.clarku.edu/~djoyce/java/elements/bookVII/propVII2.html
</aside>
• ... That s a nice proof! I think I can see daylight now! ;-)
Message 10 of 10 , Feb 7, 2006
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> <aside>
> A month or so ago I was looking into finding the greatest common
> divisor of two integers. I had a pretty crude algorithm that I had
> written some years ago. After telling a colleague about it, he very
> quickly pointed me in the right direction...
>
> Euclid's algorithm, developed around 300 BC! Very very fast on a
> computer.
>
> http://aleph0.clarku.edu/~djoyce/java/elements/bookVII/propVII2.html
> </aside>

That's a nice proof!
I think I can see daylight now!
;-)
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