So when does the new Millennium really start? Take you pick, seems to be the message coming out of the American Association for the Advancement of Science (AAAS) expo in Anaheim, USA.

Delegates at the annual meeting were treated to the thoughts on the subject of Harvard University astrophysicist Owen Gingerich.

While most people around the world will plump for 1 January, 2000, as the date to usher in a new millennium, Gingerich produced an almost baffling array of different dates.

He said the 1 January date next year could be anything from the fraction of a second that it takes an atom to vibrate to several years out.

Confused?

And just as everyone in Anaheim was scratching heads over that one he introduced a character called Dennis the Short - his real name was Dionysius Exiguus. This gentleman was a monk who, in AD 531, produced the calculations that underpin our current calendar.

Owen Gingerich: The world is suffering from "odometer syndrome"

Dennis was asked by the authorities to work out when Easter should be - not a straightforward task as the event is tied to a full moon and the vernal equinox.

Nevertheless, he realised that the pattern of how Easter bobbles back and forth between March and April takes a long time to repeat - 532 years - about the same amount of time since Christ was supposed to have been born.

Non event

But in the Dionysian cycle, the first year starts at the beginning of the first full calendar year of the reign of a new emperor. Therefore, since our calendar is based on the birth of Jesus Christ, who was born on 25 December in the year 1 BC, the millennium should be celebrated on 25 December, 2000 (remember, there was no year zero).

But even that is not the real millennium. "That is the anniversary of a non event," Gingerich said, "because Christ was already born for several years before that time."

How do we know? Because he was born when King Herod was still ruler of Judea and Herod is known to have died before AD 1. Christ must therefore have been born a few years earlier than we thought, meaning we have already missed the start of the new millennium.

If all this sounds crazy then Gingerich is pleased. He dubbed the current millennium excitement "the odometer syndrome," likening this irrational exuberance to children waiting for a car's mileage counter to change from 999 to 1000.