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History of Science Course Syllabus - Flat Earth woodcut

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LibraryThing: OU History of Science Collections HSCI 3013 - section 995 - Spring 2014

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
  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:
  4. Since a century lasts 100 years...
  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.


"The intelligent minority of this world will mark 1 January 2001 as the real beginning of the 21 century and the Third Millennium.... Those who celebrated the twin events a year too soon are also invited to join in the celebrations.... Though some people have great difficulty in grasping this... we'll have had only 99 years of this century by January 1 2000." Sir Arthur C. Clarke, author of 2001: A Space Odyssey in a 2000 interview.

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HSCI 3013. History of Science to 17th centuryCreative Commons license
Kerry Magruder, Instructor, 2004
Brent Purkaple, TA

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Many thanks to the pedagogical model developed in Mythology and Folklore and other online courses by Laura Gibbs, which have been an inspiration for this course.

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This course is currently undergoing major reconstruction to bring it into alignment with the new version of the course at Janux