# When Did the Millennium Start?

In my opinion, the simple answer is: Who cares?

I assume that everybody agrees that the “first digit change” on January 1, 2000 was an important event for everybody who uses the Gregorian calendar. So what should we call that date? I have absolutely no qualms about calling it the start of a new millennium, in spite of the fact that it was only 1999 years since January 1, 1 (Gregorian).

Some people say that they will celebrate on January 1, 2001 instead. What exactly will they celebrate? 2000 years since January 1, 1 (Gregorian)? What's the big deal about January 1, 1 (Gregorian)? Nobody believes that Jesus was born then, and because of the Gregorian reform, it's not the same as January 1, 1 (Julian).

I'm glad that people understand the difference between counting from 0 and counting from 1, but that doesn't change the fact that the “first digit change” is a big event. I feel that a lot of the 2001 people are just trying to show off their understanding of 0 versus 1.

In my opinion, it's important to look at the history to understand how the A.D./B.C. system came about. Dionysius was constructing new Easter tables. The old tables ran up to what we now call 531. The Julian Easter tables had a period of 532 years (532 = 19 * 28). So he worked backwards and came to the year we now call 1 B.C. He picked the traditional date for the spring equinox as the day of incarnation of Jesus and claimed that Jesus was born on December 25, 1 B.C. (Julian), the traditional date for the winter solstice.

So according to Dionysius, the important year was not 1 A.D., but the year before. That was the start of his Easter cycle and the year of incarnation and birth of Jesus. Traditionally, the year started on March 25, and on March 25, 2000, it was 2000 years since the day that Dionysius picked as the incarnation of Jesus (ignoring the Julian/Gregorian business). Considering that we now start the year on January 1, instead of March 25, I think it makes perfect sense from a historical point of view to say that January 1, 2000 was the start of the new millennium.

Given that Dionysius considered the year before 1 A.D. to be the starting year, it was unfortunate that the French Jesuit astronomer Denis Petau in 1627 started referring to this year as 1 B.C.

By the way, in about 500 years time, the Muslims will face the same dilemma. I still think that the first digit change is the important event, but I believe that it makes somewhat more sense for Muslims to celebrate at the beginning of their year 2001, sine that will be 2000 (Muslim) years since the year of the move to Medina.

For a good explanations of this, please read the article by Sean Oberle. I also recommend John Sullivan on the New Millennium.

Back to Helmer Aslaksen's page on Calendars in Singapore.

Helmer Aslaksen
Department of Mathematics
National University of Singapore
helmer.aslaksen@gmail.com

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