Monday, January 25th, 2010

Days and Years

When the Babylonians invented the week they made it seven days long because they thought that there were seven “planets”. They named each hour of each day after a different planet in order from slowest to fastest and then the days were named after the same planet as the first hour of each day. We still name the days of the week the same way since the names for the days come from the names of those same seven “planets” with the names still in that same order starting with Saturday as the first day of the week.

When Dionysius Exiguus invented our current year numbering in the sixth century he made a mistake in calculating when Augustus first came to power in Rome which was what he used as his starting point for calculating the birth of Jesus. As a result he was somewhere between four and seven years out. The latest Jesus can have been born is 4BC since that was the year that Herod died. Also while Aryabhata invented zero in the same Century as the AD numbering was introduced it took until the thirteenth century for that to get from India where it was invented into the west. Since the year numbering had already been in use without a year zero for seven centuries by then it was considered to be too late to go back and revise the year numbering to add it in (although other similarly drastic changes have been made to the calendar since then such as dropping several days and changing the year from starting on 21st March to starting on 1st January as was done in converting from the Julian to the Gregorian calendar).

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