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How to get a Date

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Phrases such as “in the fifth century B.C.” leave many people confused. The following notes should help you get a handle on dating notation and terminology.

1. BC, BCE, CE & AD
• B.C. or B.C.E. = “Before Christ” or “Before Common Era”; used for dates before 1 A.D.
• A.D. or C.E. = “anno Domini” (“in the year of our Lord”), or “Common Era”; refer to dates after 1 B.C.
  
  
2. In general usage and by historical convention, there is no zero year, 0 B.C. or 0 A.D.
   That is, the year before 1 A.D. was 1 B.C.
   
   
3. The first and last years of each century:
• 1 B.C. was the last year of the first century B.C.
• 1 A.D. was the first year of the first century A.D.
  
  
4. Since a century lasts 100 years...
• The first century A.D. lasted from 1–100 A.D. (inclusive).
• The first century B.C. lasted from 100–1 B.C. (inclusive).
  
  
5. Given the above, you can derive a table like the following:
   

   100–001 B.C. = first century B.C.	001–100 A.D. = first century A.D.
   200–101 B.C. = second century B.C.	101–200 A.D. = second century A.D.
   300–201 B.C. = third century B.C.	201–300 A.D. = third century A.D.
   400–301 B.C. = fourth century B.C.	301–400 A.D. = fourth century A.D.
   500–401 B.C. = fifth century B.C.	401–500 A.D. = fifth century A.D.
   600–501 B.C. = sixth century B.C.	501–600 A.D. = sixth century A.D.
   	2008 = the 21st century, etc.

   (Take a few moments to think through the above table. You'll see how it follows from the points given above. It won't take you long to become familiar with its patterns.)
   
   
6. The same reasoning used for centuries (above) also applies for millennia. If 1000 years = 1 millennium (plural = “millennia”), then:
   

   1000–0001 B.C. = first millennium B.C.	0001–1000 A.D. = first millennium A.D.
   2000–1001 B.C. = second millennium B.C.	1001–2000 A.D. = second millennium A.D.

   
   
7. It is best to use both types of notation together to avoid confusion. That is, when someone says: “in the middle of the second century B.C.”; mentally repeat to yourself: “around 150 B.C., in the second century.”
   
   
8. Just when you think you have it all figured out.... Astronomers use a different and more rational convention, inserting a zero year. That is, the historian’s 1 B.C. becomes the astronomer’s 0 year. Therefore, x B.C. for the historian = (x–1) B.C. for the astronomer. In this course, we'll use the historian's reckoning, but beware of this possible discrepancy if you find resources about ancient astronomy prepared by astronomers.

	HSCI 3013. History of Science to 17th century Kerry Magruder, 2004-08 Report typos or broken links Many thanks to Mythology and Folklore and other online courses developed by Laura Gibbs.	Search course websites:
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