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### Millennium and the Year 0

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Date: 01/03/99 at 22:39:33
From: Katie
Subject: Millennium

I am doing a science project on when the new millennium really begins.
I already know that it truly begins in the year 2001 because there was
no zero year between B.C. and A.D. I was wondering if you knew why or
could give me some sites about why the early mathematicians didn't let
a whole year pass before naming it one. I would also appreciate any
other information you could give me about my project. I have already
looked it up under many different subjects in Encarta 98 and tried
tons of different ways to get information on the Web, but I'm having
trouble finding information.

Thanks,
Katie
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Date: 01/04/99 at 08:47:26
From: Doctor Rick
Subject: Re: Millennium

Hi, Katie, welcome to Ask Dr. Math!

Thanks for asking this question, it's a good one. To answer it, you
will need to look at the history of the calendar, and the history of
math.

BC dates were not used in the BC era. BC means "before Christ"; that
is, before the birth of Christ. Before he was born, people (even the
relatively few people who were expecting his birth) did not know just
when it would be, so they couldn't date their calendars that way! As a
matter of fact, AD and BC were not invented until around AD 525, by
Dionysius Exiguus.

In AD 525, people in Europe didn't have a clear idea about negative
numbers. In fact, it wasn't until 1657 that a mathematician (John
Hudde) used a single variable to represent either a positive or a
negative number. For all those years until 1657, positive and negative
numbers were handled separately. Nobody drew a number line with
positive numbers on one side, negative numbers on the other, and 0 in
between.

Let's get back to Dionysius. He identified the year 1 AD ("1 Anno
Domini," the first year of the Lord) as the year that Christ was born
(he was probably off by 4 to 6 years). The previous year was 1 BC, the
first year "Before Christ." (I have not figured out why one
abbreviation is in Latin while the other is in English.)

Dionysius would not have thought of 1 BC as the year -1. He would not
have thought of putting BC and AD together on a number line (timeline).
BC and AD were two separate cases. To find the time between two AD
dates, you would take their difference. To find the time between an
AD date and a BC date, you would add them and subtract 1. This would
not be seen as a problem. It's just the way they solved other kinds of
problems (like quadratic equations, if you've seen them) - as a set of
special cases.

I have found some Web sites that can give you more information on the
things I have said.

Here is an interesting Web page about the origin of the calendar (see
the section "Century and Millennium"):

Larry Freeman's Calendar Origin Page
http://ourworld.compuserve.com/homepages/Larry_Freeman/calendar.htm

Here is another (see the section "The start of Anno Domini Dating"):

Historical Ecclesiastical Calendar:
Easter and its Relevance for Chronology

Here is a Web page about the origin of negative numbers:

Negative Numbers - Kevin Brown
http://www.mathpages.com/home/kmath298.htm

One of Jeff Miller's pages is my reference for John Hudde:

Earliest Uses of Symbols for Variables
http://jeff560.tripod.com/variables.html

- Doctor Rick, The Math Forum
http://mathforum.org/dr.math/
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Associated Topics:
High School History/Biography
Middle School History/Biography

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