What do BC, AD, BCE, and CE mean?

In our dating system, BC means "before Christ" and AD means "Anno Domini," a Latin phrase meaning "in the year of our Lord." AD does not mean "after death [of Christ]." CE is a modern designation that means "Common Era" and is meant to replace AD. In other words, 2017 AD and 2017 CE mean the same thing. BCE means "Before Common Era" and is meant to replace BC.

There have been numerous calendars used in history, including but not limited to the Lunar Calendar, the Egytpian Calendar, the Roman (Julian) Calendar, and the Gregorian Calendar. Dionysius Exiguus (c. 465 AD - c. 530 AD) is known as the inventor of the AD era system, used to number the years of both the Gregorian and the Julian Calendars. Dionysius was trained as a mathematician and an astronomer. In 525 AD, Pope John I asked Dionysius to extend the existing Easter tables. This was an attempt to help unite the eastern and western branches of the Catholic Church. Another intent of his system was to replace the Diocletian era system used in the old Easter table. Dionysius and other Catholics did not desire Easter to be in any way associated with a tyrant who persecuted Christians.

Dionysius' AD dating method was based upon what he determined to be the date of Jesus Christ's birth (Matt 1:18); though today numerous biblical scholars believe Jesus' birth was actually closer to 6-4 BC, and not 1 AD. Dionysius BC and AD designations are still used in the Gregorian calendar; attributed to Aloysius Lilius (c. 1510-1576).

It is absolutely fascinating that the designations BC and AD approximate the time when God became incarnate in the person of a Jesus Christ and walked upon the face of this earth. "But when the fullness of time had come, God sent forth his Son, born of woman, born under the law" (Gal 4:4). Every time someone writes or says the date of their birth they inadvertently focus upon the existence of God in the flesh (John 1:14). Perhaps our next conversation with an Atheist should begin with, "I was born in ????, in what year were you born?"