Numbering Years

On ancient calendars, years were generally numbered according to the year of a ruler's reign, for example, the third year of Hammurabi’s rule.  About AD525, a Christian monk named Dionysius Exiguus suggested that years be counted from the birth of Christ.  The year 2011 can also be written as AD2011. AD refers to the term anno Domini, or “the year of the Lord.”  The years before the birth of Christ are numbered backward from his birth.  The year before AD1 was 1BC, or one year “before Christ.”  When referring to dates before the birth of Christ, the higher the number the earlier the year. Since years are marked from a set point known as 1 (there is no year 0), 3500BC was about 5500 years ago.

Non-Christians often use the term CE in place of AD. CE refers to “Common Era” or “Christian Era.”  BCE can describe the era preceding the Common Era.  This can mean “Before the Common Era,” or “Before the Christian Era.”

There are ten years in a decade, one hundred years in a century, and one thousand years in a millennium.  This is considered the twenty-first century of the Common Era.  On December 31, 1999, many people celebrated the coming of the new millennium, but the millennium did not end until December 31, 2000.  This is because the calendar we use does not have a year called 0.

We also use terms such as era or epoch to describe periods of time.  A geologist is someone who studies how the earth has changed, and for a geologist, an era might last millions of years.  In this class an era will be any significant period of time.  For example, you are in the middle school era of your life.  You may see photographs of people wearing different styles of clothing that reflect the era when the pictures were taken.  An epoch is a particular moment.  Your thirteenth birthday will be the epoch that begins your teenage years. 

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