Re: Why do Oracle dates go only up to 4712 A.D. is there some technical reason for such a specific date

Based on the Julian Calendar..

Hail Caeser.

Astronomical Julian Days
Although Joseph Justus Scaliger was, as noted above, one of the founders of the science of chronology, it seems he did not invent the Julian day number system. Its inventor was the astronomer John W. F. Herschel. Lance Latham writes:

"It remained, however, for the astronomer John F. Herschel to turn this idea [of Scaliger's] into a complete time system, rather than a method of relating years. In 1849, Herschel published Outlines of Astronomy and explained the idea of extending Scaliger's concept to days." — The Standard C Date/Time Library, p.42.
Following Herschel's lead astronomers adopted this system and took noon GMT -4712-01-01 J (January 1st, 4713 B.C.) as their zero point. (Note that 4713 B.C. is the year -4712 according to the astronomical year numbering.) For astronomers a Julian day begins at noon and runs until the next noon (so that the nighttime falls conveniently within one "day", unless they are making their observations in a place such as Australia). Thus they defined the Julian day number of a day as the number of days (or part of a day) elapsed since noon GMT (or more exactly, UT) on January 1st, 4713 B.C., in the Proleptic Julian Calendar.

Thus the Julian day number of noon GMT on -4712-01-01 (Julian), or more casually, the Julian day number of -4712-01-01 itself, is 0. The Julian day number of 1996-03-31 is 2,450,174 — meaning that on 1996-03-31 2,450,174 days had elapsed since -4712-01-01 (or more exactly, that at noon on 1996-03-31 2,450,174 days had elapsed since noon on -4712-01-01).

A decimal component may be used, so that JD 0.5 is the midnight point separating -4712-01-01 J and -4712-01-02 J, JD 1.25 is 6 p.m. on -4712-01-02 J, and so on.

mosene wrote in message ...
>why 4712 and not something else?
Received on Mon Nov 22 1999 - 16:02:43 CST