The other Millennium Bug

Keith Rankin, 8 April 1998


As Wellington's Religious Studies professor Jim Veitch pointed out (5/4/1998, National Radio, "A Question of Religion"), the sixth century (ie living in the "five-hundreds") Christian monk Exiguus made two mistakes. Although well-intentioned, his errors haunt us at the end of each millennium, just as the errors of the first computer programmers haunt us at the end of this millennium. In Exiguus's case, the problem occurs at the end of each decade [ie which decade was the year 1990 in?] but is more contentious at the end of a century or millennium.

Around the year 1250 in the calendar of his day (the Roman calendar) Exiguus estimated the date of Christ's conception, and called it 1 January, 1 AD. He made an historical error (Christ was in fact born before that date) and an arithmetic error (he should have called that date 1 January, 0 AD). It also seems that he made a third physiological error. The average time between conception and birth is 38 weeks. Thus the birth of Christ would have been in the last week of November (then the ninth month), not December.

In creating a new AD scale, Exiguus also created a BC scale as a worthy but unsuccessful attempt at dealing with the negative number problem.

Today we have to make the best of Exiguus's legacy. We celebrate Christmas on 25 December knowing that Christ was not actually born on that date, much as we celebrate the Queen's birthday on a date which is not her birthday. Furthermore, we accept that the first day of the first millennium AD was just an ordinary day; nothing special happened. And we accept that all AD dates before 550 AD (and all BC dates) are purely historical artefacts; nobody ever set their calendars to the year 50 BC, 50 AD or 500 AD.

We also take it for granted today that the first millennium AD was the zero-thousands, that the second millennium AD is the one-thousands, that the first century AD was the zero-hundreds, that the twentieth century AD was the nineteen-hundreds. Thus it follows that the two-thousandth year AD is the year 1999, and that the third millennium begins as the 2001st year (ie 2000) begins. When we consider the age of any person or any thing, they are aged 99 during their 100th year.

Rather than considering the BC scale as the negative of the AD scale (which it isn't), we should just accept that AD and BC are two separate scales, one of which counts forwards and one of which counts backwards. Thus any year between the big bang and the demise of the universe can be given a number in either scale; indeed in any of the many other non-Christian scales as well. Thus the year 4 BC was also the year -3 AD, 1 BC was 0 AD, 0 BC was 1 AD, -3 BC was 4 AD, and -1999 BC will be 2000 AD.

So when does the third millennium begin? It all depends on which scale you wish to use. If you prefer to use the backwards counting BC scale, the third millennium begins on 1 January -2000 BC (which also happens to be 1 January 2001 AD). For those who use the AD scale, the third millennium starts at the beginning of the 2001st year AD, which is of course 1 January 2000.

If Exiguus had not made his second error, the date today would be 8 April 1997 (not 1998). If he hadn't made his first error, we would already be in the third Christian millennium. But he did make these errors. As a result, we enter the third millennium 633 days from now.


PS [29 January 1999] I received an email from Jim Blowers (from Virginia, USA) about his item "The Millennium begins with the Year 2000".


© 1998

Rankin File | 1998 titles