We use a dating system called the Gregorian calendar.
It was put together to give us an accurate estimate to the tropical year (time required for the Sun, beginning at a chosen ecliptic longitude, to make one complete cycle of the seasons and return to the same point on the ecliptic longitude).
Most of Europe (Well countries under Papist rule) stopped using the Julian calendar (named after the great Ceasar) and switched over to the Gregorian starting in 1582, at which point the 10 day slip between the actual time of year and traditional time of year on which calendar events occurred became really misaligned and were having a major effect on calculating Easter and other holidays.
So, Pope Gregory XIII decreed that the day after October 4, 1582 would be October 15, 1582, the Papist countries of France, Spain, Portugal, and Italy complied.
Various Catholic German countries (Germany was still not yet one country and still full of small autocratic states), The Netherlands (The Flemish Belgians had not yet split and created Belgium), Switzerland , Austria and Hungary followed a few years later. The other Protestant German countries adopted the Gregorian calendar in 1700.
By this time, the calendar was out by 11 days.
England (and the American colonies who committed treason 20 years later) finally followed in 1752, and Wednesday, September 2, 1752 was immediately followed by Thursday, September 14, 1752. This change resulted in widespread calendar riots and the populace demanding "Give us the eleven days back!" as they lost pay. Russia adopted it in the early 1900's and China and India in the later in the 20th Century.
It has a few problems - the cycle of the Earth and Sun sometimes slows down. For instance I've read before that we have a missing day every century, owing to the rounding up of 365 days, 5 hours, 48 minutes, 45.25 seconds to 3651/4 days in the Julian calendar that was used before the Gregorian one.
In addition, the new calendar is still losing 26 seconds from the solar cycle annually (I need to verify this). Add to the fact that the Julian calendar made a leap of 67 days to sync with the solar cycle, shortly after Julius Ceasar died there was confusion with the methodology involved, with the most damaging being the three years leap years (instead of the now common four).
So, Anyway I have this theory based on a loose calculation of this Great Cycle in its entirety against the modern calendar, taking into account the faults and adjustments incorporated into it give me the feeling that the prophesised date would be sometime around a 3 month period October to December , 2011 (or thereabouts) - Stop rolling around in laughter - I'm wondering if when people tell us the Mayan calendar says it will all end it in 2012 have they taken all of this into consideration.
Actually, I remember seeing one of those disaster movies where the Gov't knew it was going to happen and the President was black! (Maybe, we were being prepared). What if the Mayan calendar just ends as there was no more space on the calendar as 5,125 years is lot to map out;-)
I found this interesting as this is within weeks of Elenin the comet projected perihelion (to you and I thats the closest point to the Sun in a planet's orbit - the furthest point is called aphelion) and, more alarmingly, within 12 days of its forecasted perigee (closest orbital distance to the center of earth) and another comet in November called Yu 55.
What so special about the Elenin and YU 55 comets? (I hear you ask) Well, hmmmmm, That's another story In the meantime you can go search on the web and you'll see people are getting all excited - (Remember I didn't say anything about Lizards;-)