CULTURE WATCH : Before There Were Daytimers

You may not realize it, but the calendar is one of the oldest and most reliable timekeeping devices of our civilization. It dates back to 1582, when Pope Gregory XIII set out to reform the Julian calendar, the calendar established by the ancient Egyptians and modified in 45 BC by Julius Caesar.

The Julian calendar was based on the number of days--365.25--between successive risings of the bright star Sirius just before sunrise. To synchronize with the seasons, the Romans added a 366-day leap year every four years.

The problem with the Julian calendar was that it was 11 minutes longer than the then-adopted length of the tropical year (the period from equinox to equinox) of 365.2421 days. That discrepancy worked out to a gain of more than 10 days in 1,600 years. In 1582, for example, the first day of spring was March 11.

Pope Gregory’s reform recalibrated the calendar by omitting 10 days in October. Thus, Oct. 4, 1582, was followed by Oct. 15. The modification brought everything back in step with the seasons.

Eventually, the years cycle around and the days and dates match up again with previous years. A calendar from 1981 would have sufficed for 1992, and will be useful again in 1998 and 2009.