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

> <aside>

That's a nice proof!

> 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>

I think I can see daylight now!

;-)