Les Mercredis d'Endoume / La longue histoire de notre calendrier de 45 av. J.-C. à 2100...

Speaker: Christian Garing, agrégé and PhD in physics

Summary: How do we define a year, how do we measure it, and how accurately?

Why did Julius Caesar reform the Roman calendar? When and how was the date of Easter established? Who chose year 1 as the starting point of our calendar, and why did astronomers introduce a year 0?

In 1582, why was the day after Sunday, December 9… December 20? Why is Christmas celebrated on January 7 in Orthodox churches? And why will the year 2100 not be a leap year, even though 2000 was?

A story where astronomy, science, religion and politics intersect, helping us understand how the calendar we use today came to be.