Calendar History and Ancient Ways of Keeping Time

A.D.

The initials A.D. (used with or without periods) is an abbreviation for the Latin "Anno Domine", which translates to "the Year of Our Lord," referring to years after the birth of Jesus Christ.

A.H. (Anno Hegirae)

A.H. (Anno Hegirae) is the calendar designation for the Muslim religion.

Archaeoastronomy

Archaeoastronomy is the the study of ancient methods and reasons for studying the stars and planets

BP (or B.P.)

Archaeologists use the term 'BP' to mean 'years before humans began to screw up the atmosphere by testing nuclear devices'.

BC (or B.C.)

The term B.C. is used by nearly everyone in the United States to mean dates in the Julian Calendar before the birth of Christ, or at least before the date once thought to be that of Christ's birth (the year 0).

BCE (or B.C.E.)

BCE stands for "Before the Common Era" and it is basically equivalent to "BC", except that it doesn't have the Christian religious connotations of BC.