Happy Easter & Happy Passover!

First Posted on Good Friday, April 15, 2022 /  Erev Pesach, Yom Shishi, 14 Nisan, 5782.

By: David Orenstein, Danforth CTI, Retired

By happy coincidence, this day is important for both Easter and Passover: Good Friday today, and the first Passover Seder tonight, after sundown.

But how do we know when it’s Easter or when it’s Passover?

Since this blog post is being hosted by the British Society for the History of Mathematics website, let’s hear what a historic British authority on Christian Calendrics had to say:

“ ‘To the most excellent and illustrious lord, King Nechtan [King of the Picts], from Abbot Ceolfrid [of Wearmouth and Jarrow] – Greetings in our Lord.

“ ‘In response to your devout enquiries… I am most willing… to explain the Catholic observance of Easter.

“ ‘After the sacrifice of Christ our Passover, the Lord’s Day [Sunday]  (which the ancients called the first day [<<Yom rishon>>, in Hebrew] after the Sabbath) was made holy for us by the joy of his resurrection and … the Apostles established this day for the Easter feast…. [A]ccording to the Law, the first month of the year [in that period, April in the Christian calendar and Nisan in the Jewish] and its fourteenth day and the evening of that day should be awaited. And if by chance that day fell on the Sabbath [i.e. Saturday] … all churches throughout the world, who constitute the one Catholic church, should prepare bread and wine as a sacrament of the Body and Blood… in the solemn celebration of Easter.

“ ‘Therefore if it could be … that a Sunday should always fall on the fifteenth day of the first month, that is, on the fifteenth appearance of the moon, we should be able always to celebrate our Easter at the very same time as the ancient people of God, as we do by the same faith, although by a different kind of sacrament. But because the days of the week do not keep pace with the phases of the moon, the apostolic tradition… decreed that, when the first month came round of the evening of its fourteenth day, they should wait further for the Sunday, from the fifteenth to the twenty-first day of that month. And on whatever of these days Sunday should occur, Easter should be celebrated on that day, because this falls within the seven days of unleavened bread, or at any rate occupies some of these days. For even if only one of them is included, that is the seventh day… no one can accuse us of not keeping the Easter Day, … in the third week of the first month as the Law decrees.’ ” (Bede 1968, pp. 315-319).

Well, that’s Bede’s explanation (in English translation from the original Latin) of the date of Easter, from about 1300 years ago. So how do we figure out when it’s Passover (Pesach)?

Pesach starts on the 15th of Nisan every year, and lasts for seven more days, that is until the 22th of Nisan at the end of the [Jewish] day. Or for this Jewish year: from Erev Shabbat, 15 Nisan, until Havdalah, Yom rishon, 23 Nisan, 5782.

In the Civil Calendar that means, for 2022/5782 from 7:43 pm on Friday, April 15, until 7:52 pm, on Saturday, April 23. That’s Toronto time. For London, England, and for Jerusalem, Israel, the times are respectively, 7:39 pm & 7:51 pm and 6:27 pm & 6:33 pm. All times are local Daylight Savings Time. (Again, we render homage to Sandford Fleming.)

An interesting note is that Pesach 5782 ends on St. George’s Day 2022. By the way, our previous major Jewish holiday (<<Yom tov>> = lit. “Day good”), Purim, 14/15 Adar II, 5782, coincided with St. Patrick’s Day, March 17, 2022. Both St. Patrick’s Day and Purim celebrations encourage significant happy consumption of alcoholic drinks.

Nisan? What’s that?

“Nisan” is the one of the twelve names for the months in the Jewish (Hebrew) Calendar, that I posted about on September 3, 2021, just before Rosh Ha-Shonah, 5782, and based on the work of retired University of Ottawa mathematics professor (and fellow member of CSHPM), Edward L. Cohen. (“Jewish Calendar in Canada”)

Nisan, with its 30 days, is the eighth month of the current Jewish year, 5782. Rosh Ha-Shonah (literally “The Head of the Year” in Hebrew) is the holiday that marked the Jewish New Year. By our traditional understanding, Rosh Ha-Shonah 5782, marked exactly 5781 years since the moment of Creation, on Yom Shlishi (Third Day), the 1st of Tishrei, 5782 :: Monday/Tuesday, September 6/7, 2021.

Back in September, I also mentioned some of the other Jewish holidays we commemorated, besides Rosh Ha-Shonah, during the month of Tishrei, 5782, (September 6 – October 6, 2021):

Yom Kippur – The Day of Atonement: 10 Tishrei, 5782 (September 16-17, 2021),

Sukkot – Fall Harvest Festival: 15-20 Tishrei, 5782 (September 20-26, 2021),

Simchat Torah – Anniversary of Receiving the Torah at Mount Sinai: 23 Tishrei, 5782 (September 28-29, 2021).

In Nisan, 5782, we’ve already celebrated Shabbat Ha-Gadol (The Great Sabbath), on the 8th of Nisan, the last Sabbath before Pesach. At Synagogue, we commemorated Refugee Shabbat on Erev Shabbat, the evening of Friday, April 8. On the morning of Saturday, April 9, we studied the weekly Torah Parshah, Metzora (Leviticus / Va-Yikra’: 14.1 -15.33) and the Haftorah readings from the Prophets / Nevi’im, both Malachi 3.4-24 and 2nd Kings 7.3-20. This was under the leadership of not only the rabbi, but also the cantor and the two B’nei Mitzvah. A young woman who became Bat Mitzvah and a young man who became Bar Mitzvah.

During Pesach, on the second day, 16 Nisan, we will begin the Counting of the Omer, for a week of weeks. That is, seven times seven days, 72 days = 49 days. This covers the stretch up until Shavu’ot: Yom Rishon, 6 Sivan, and Yom Sheni, 7 Sivan (Saturday, June 4, to Monday, June 7).

In between, there will be many more holidays for us to commemorate. But those are other stories!

Chag Pesach Sameach! Happy Easter!



Bede (1968), revised translation edition by R. E. Latham, translated by Leo Sherley-Price, 1955, first composed in Latin, 731 CE., A History of the English Church and People in Penguin Classics. Penguin Books, Harmondsworth, England and Markham, Ontario, Canada. 364 pp., incl.9 pp. Notes, 3 pp. Genealogy of the English Kings, 12 pp. Index.

Edward L. Cohen:

(1994) “The Hebrew Calendar Simplified” Proceedings of the Canadian Society for the History and Philosophy of Mathematics, 7: 50-57

(1996) “Gregorian Dates for the Jewish New Year” Proceedings of the Canadian Society for the History and Philosophy of Mathematics, 9: 79-90

(2000) “Adoption and Reform of the Gregorian Calendar” Math Horizons 7(3): 5- 11

(2001) “The French Republican Calendar” Proceedings of the Canadian Society for the History and Philosophy of Mathematics, 14: 32-40

(2002) “The Mayan Calendars” Proceedings of the Canadian Society for the History and Philosophy of Mathematics, 15: 36-57

(2003a) “Calendars of the Dead-Sea-Scroll Sect” Cubo Matemática Educacional, 5(2): 1-16

(2003b) “The Islamic Calendar” Proceedings of the Canadian Society for the History and Philosophy of Mathematics 16: 116-130

(2005) “The Iranian Calendar” Proceedings of the Canadian Society for the History and Philosophy of Mathematics 18: 64-74

(2006) “Ancient Egyptian Calendars” Proceedings of the Canadian Society for the History and Philosophy of Mathematics 19: 64-79

(2007) “Important Indian Calendars” Proceedings of the Canadian Society for the History and Philosophy of Mathematics 20: 83-93

(2008) “Chinese and Japanese Calendars” Proceedings of the Canadian Society for the History and Philosophy of Mathematics 21: 53-72

(2010) “The Roman Calendars” Proceedings of the Canadian Society for the History and Philosophy of Mathematics 23: 72-84



1. My other Time related blog posts:

a) May 21, 2021, “Time Zones I: ‘Half an Hour Later in Newfoundland’ ”.


b) February 20, 2022. “Time Zones II: Sir Sandford Fleming and Standard Time”.


c) March 30, 2022, “Time Zones III: Sir Sandford Fleming at Home. My Home, That Is!”


2. My CSTHA Calendrics Blog Posts:

a) March 5, 2021, Mi’kmaw Calendar:


b) 3, 2021, “Jewish Calendar in Canada”


c) 3, 2022, “Happy New Year! Happy New Month!”


3. Canadian Society for the History and Philosophy of Mathematics (CSHPM) website: