The first day of the 21st century will be January 1, 2001. Neither the present century nor the second millennium will end with 1999, as is widely assumed.

Why?

Suppose you were counting out one hundred pennies to make a dollar. The 100th penny you counted would be the last penny counted toward the dollar. Similarly, if you were counting out two thousand pennies to make twenty dollars, the 2,000th penny would be the last one counted, the end of the series.

Since we begin counting with number 1, centuries begin with years ending in 1, not with years ending in 0. It doesn't make sense to begin counting with zero, because zero stands for the absence of anything to be counted.

In the year 2000 we can celebrate the 100th year of the 20th century, but we'll have to wait until 2001 for the first year of the next century. In AD 2000 we can also celebrate the 2,000th year of Christ. Contrary to the beliefs of some infallible persons, however, this will not be the 2,000th anniversary of the birth of Christ.

The Catholic Church is planning a Great Jubilee for the year 2000, apparently under the mistaken assumption that AD 2000 marks a noteworthy anniversary of Christ's appearance in the world. Here is an excerpt from Pope John Paul II's Apostlic Letter, "As the Third Millennium Draws Near":

15. In the lives of individuals, jubilees are usually connected with the date of birth; but other anniversaries are also celebrated....

In view of this, the 2,000 years which have passed since the birth of Christ (prescinding from the question of its precise chronology) represent an extraordinarily great jubilee, not only for Christians but indirectly for the whole of humanity, given the prominent role played by Christianity during these two millennia. It is significant that the calculation of the passing years begins almost everywhere with the year of Christ's coming into the world, which is thus the center of the calendar most widely used today....

16. The term jubilee speaks of joy; not just an inner joy but a jubilation which is manifested outwardly.... Hence the year 2000 will be celebrated as the Great Jubilee.

But even if we ignore the fine points of actual chronology, and take the year 2000 as symbolic for the 2,000th year of the Christ, it is still not the 2,000th anniversary of his birth.

December 25, 2000 could be Jesus' 2,000th birthday only if he were born on December 25, 0000. But there was no year zero. The early sequence of years goes from 1 BC immediately to AD 1. No one could have counted the "year zero," because zeros stand for nothing to count.

Astronomers nevertheless use a zero-year for some of their calculations. Their counting device replaces AD years with positive numbers, and years BC with negative numbers. Converting to a number line in this way, they feel compelled to recognize a zero-point between the negative and positive numbers. They thus equate AD 1 with year +1. They number the preceding year (1 BC) as year 0, and they take the year preceding that (2 BC) as year -1.

What conclusion is to be drawn from all this?

It is too easy to ridicule someone, especially a church, for imperfect counting. It is more interesting to recognize that people attach greater significance to numerical landmarks in time, like the year 2000, than to actual chronology. And why not? Isn't a round number like 2000 more easily embraced by the imgaination than an odd, technically correct counter like 2001?

To us, AD 2000 means the beginning of a new century, a new millennium, and a special anniversary of the birth of Christ. These meanings will affect our lives and our celebrations. They will have a "practical reality" even for those of us who recognize the merely symbolic nature of time's landmarks in the imagination.

The conclusion to be drawn, then, is a significant point about the nature of the human activity of time-keeping: that time-keeping is less an exercise in counting, than an art of the imagination.

A note from Jay Gary:
A strong case has been making the rounds for the past 18 years putting the birth of Christ in 3 B.C. Ernest Martin, in his book, The Star that Astonished the World (ASK Publications, Portland, OR, 1996) presents a well researched and argued case for this from astronomy and recent finds supporting the later date for the death of Herod. As a result, the Griffith Observatory in Los Angeles, and many other planetariums no longer use the 4 BC constellations in their Christmas shows, but highlight the August/September 3 B.C. birth constellations and the December 2 B.C. skies, showing the "star of Bethlehem."