And now for something completely (honest!) different. Mike Scott explains why the world isn't quite the same age as you thought it was.

Superfluous Chronology

The debate about the start of the next millennium has already started, and will continue raging for years. Is it 1 January 2000 or 1 January 2001? This article does not address that question (since the Plokta cabal know it's 1 January 2001), but instead observes that a much more significant millennium is approaching rapidly, and its exact date is much more open to debate.

In 1658, Archbishop James Ussher, Primate of All Ireland, wrote, well, a lot of tedious stuff which is available to those of a pedantic and masochistic disposition upon application to Plokta HQ, but including:

-- J. Ussher, The Annals of the World iv

710 of the Julian Period is, famously, 4004 B.C. The Guardian has recently observed that the 6000th anniversary of the creation of the world is thus on 23 October 1996. Being journalists, moreover being Grauniad journalists, they have observed wrongly. Most dramatically, there is of course no year 0 (an unfortunate error by Dennis the Little and the Venerable Bede), so it's only the 5999th anniversary this year. One might therefore naïvely expect that the seventh millennium of the world starts on 23 October 1997.

Unfortunately, it's a lot more complex than that. To reach a more accurate determination, we need to delve back into the history of the calendar. For most of what follows, I am indebted to the Calendar FAQ (Frequently Asked Questions), version 1.1, posted to the Internet newsgroup sci.astro and copyright by Claus Tøndering, claus@tondering.dk. Some calendar conversions were performed by Roger Wells, without a safety net.

When Julius Caesar became Roman emperor, the calendar was in a mess. The standard year was 355 days long, and every other year they added an extra month called Intercalans (later known as The Scottish Month) of 22 or 23 days in order to keep it more or less in step with the sun. However, the priesthood failed to keep things straight, largely because they took bribes from the greetings card manufacturers and umbrella merchants to make certain years longer or shorter and thus maximise their sales. In 45 BC, Julius Caesar, who was fed up with always having dreadful weather on the Spring bank holiday, reformed the calendar to have 365 days in a year, and to double the sixth day before the Kalends of March every third year to keep it matching the sun. In order to set things straight, 46 BC had to have 445 days and fifteen months (including The Scottish Month, Undecember and Duodecember) to make up for all of the problems that had previously afflicted the calendar. This remains an unbeaten world record.

The assiduous reader will have noticed a problem. Leap years every third year was a mistake, which was soon spotted, and after 9 BC they didn't have any more until 8 AD, at which point they started having them every four years. It is still true that the extra day added is the sixth day before the Kalends of March, which in new money is February 24, and not February 29. Saints' days between 24 and 28 February in normal years are a day later in a leap year. However, the EU (as one might expect) has decreed that from 2000 AD, the extra day in leap years will be 29 February, not 24 February.

The Julian calendar proved almost adequate until the sixteenth century. Unfortunately, it resulted in years that were a few minutes too long, and gained one day against the sun every 128 years. By the sixteenth century, it was ten days out of step. Pope Gregory XIII, who was tired of the miserable weather on Spring bank holidays, reformed the calendar to omit the leap day in every century year, except those divisible by 400, and the ten extra days were dropped from the calendar -- so, in Italy, 4 October 1582 was followed by 15 October 1582. The rest of the Roman Catholic world rapidly followed suit, but the Protestant countries would have nothing to do with this evil popish plot. Archbishop Ussher was a staunch Protestant, and at the time that he wrote the British Isles were still using the Julian calendar. This explains why he placed 23 October as the autumn equinox in 4004 BC -- the Julian calendar was over thirty days out of step with the sun in 4004 BC, and his astronomical tables were well aware of this.

However, in the eighteenth century, under pressure from the ice cream sellers, the Protestant countries finally changed to the Gregorian calendar, by which point they had eleven days to drop. Britain went straight from 2 September 1752 to 14 September 1752. You may have heard the jokes about changing gradually from driving on the left to driving on the right. Sweden decided to make the calendar change gradually by having no leap years at all between 1700 and 1740, at the price of having forty years of being out of step with everyone else. So in 1700, they had no leap year. Unfortunately, in 1704 and 1708 they forgot, and had leap years anyway. So in 1712, they converted back to the Julian calendar by having a double leap year with 30 days in February. And in 1753 they dropped all eleven days at once, the same as everyone else.

The real holdouts were the Greek Orthodox countries, who are far enough south to have nice weather on the Spring bank holiday anyway and didn't change until the early 20th century, by which time they had to drop thirteen days. Greece, being Greek, changed to a slightly different calendar, under which century years are leap years only if they leave a remainder of 200 or 600 when divided by 900. Nobody will notice the difference until 2800 AD, which will be a leap year in the rest of the world but not in Greece, and in which all Greek computers will crash and it will piss down all day on the Spring bank holiday.

The other great advance of the Gregorian calendar was to improve the calculation of Easter and bring it closer to the real full moon. The calculations are now sufficiently complicated (and tedious -- details available upon application to Plokta HQ) that the exact dates for Easter repeat only every 5,700,000 years. Follycon, in 1988, was so called because Good Friday fell on 1 April that year. I now announce a bid for Follycon 2 in 5701988 AD, the next occurrence of the same position in the great Easter cycle.

But I digress. Back to Archbishop Ussher. The discrepancy between Julian and Gregorian calendars is now up to thirteen days, and 23 October 1997 on the Julian calendar is 5 November 1997 on the Gregorian calendar. This is undoubtedly the date that Ussher would have picked as the 6000th anniversary, and he would also have appreciated holding the anniversary on the same day as a well known Catholic gets burned in effigy. However, the sun disagrees, and you will note that 5 November is not particularly close to the autumn equinox. 23 October 4004 BC under the Julian calendar is 21 September 4004 BC under the Gregorian calendar, and the 6000th anniversary is of course 21 September 1997 AD, which demonstrates the improved accuracy of the Gregorian calendar by still being the autumn equinox 6000 years later. As well as being astronomically accurate, this has the added advantage of being a Sunday, making celebrations more practical. Now all you have to worry about is fitting 6,000 candles onto the cake...

So you now know on what date or dates to celebrate the Usshering in of the seventh millennium of the world. The only remaining question is: after over two millennia of fiddling with the calendar, why is the weather still so dreadful on Spring bank holidays?

-- Mike Scott, Spring bank holiday 1996, raining