M stands for millennium or thousand years, in this case the third millennium of the Common Era. January 1st, 1999 is two years exactly before the start of the next millennium.
Yes, I know must folks think the next millennium will start in the year 2000, but It isn't so. So why am I covering this in an astronomical publication? Time, from the rotation of the earth to the revolution of the earth about the sun is determined by astronomers. Although counting the days and years is usually a religious or political function.
Getting to the case in point, when does the 21st century and the 3rd millennium really start? At 0 hours Universal Time (UT) January 1, 2001. That's 7 p.m. Eastern Standard Time, December 31st, 2000. The reason the millennium starts with the year 2001, rather than 2000 is because our calendar reckoning starts with the year 1. 2000 is the 2000th year before starting another millennium. It's like counting on your fingers and toes. You don't have to remove your shoes and socks to count until you reach 11.
Who started this calendar with no year zero? The blame or credit, as the case may be, goes to Dionysius Exigus, known to his friends as Dennis the Little. He was an abbot of a monastery in Rome in the 6th Century. The year numbering of the time was from the ascendancy of the Roman Emperor Diocletian. He didn't want the calendar reckoning based on this particularly nasty persecutor of Christians. The year reckoning in Rome before Diocletian was counted back to the legendary founding of Rome seen with the initials A.U.C. What Dionysius was after was a time reckoning based on the birth of Christ. He calculated the Incarnation of Jesus occurred on March 25, 753 A.U.C.
Therefore his birth was December 25, 9 months later in AD. 1. AD. being "Anno Domini" or "Year of our Lord". This is being increasingly referred to as CE. or "Common Era". The year before AD. 1 was set as 1 BC. Originally BC. "Before Christ" was AC. "Ante Christum", meaning the same thing. Anyway there was no year 0.
By counting years starting with 1, one completes a decade, century, or millennium with a year ending with 0. The first year of the next decade, century, or millennium starts with a number ending with 1.
Despite all these great reasons to celebrate the millennium New Years Eve 2000, all the big blowouts will be on December 31, 1999. In any case on either date I'll be home by the phone supporting my client banks through their year end processing, as I have for the past more than 20 years.
This year, like many others in the past 30 years started a second late. That's because a leap second was added to the time stream just before 0 hours UTC (Coordinated Universal Time) January 1, 1999. It's due to the earth slowing rotation. The world is now timed by atomic clocks, much more accurate than the earth as a timekeeper. However our clocks are geared to the earth's rotation with respect to the sun. Therefore UTC has to be kept close to the earth's actual rotational rate, otherwise the sun might set at noon at some future date. That's where leap seconds come in. It takes actual astronomical observations to track the actual rotation of the earth with respect to the atomic clocks.
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