Calendar standards
The purpose of this article is to describe the necessary background information to understand time and date issues on the Internet and in computer clocks.
Contents
Western time standards
The western time standards dividing the year into 12 months, the day into 24 hours or 12 hours AM and 12 hours PM, the hour into 60 minutes and the hour into 60 seconds derived from the Mesopotamia[1] using the sexagesimal[2] or base 60 numeral system.
- Note:
- The base 60 systems is a highly composite number as 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30 and 60 are factors.
Julian calendar
The Julian calendar[3] was introduced by Julius Caesar in 46 BC and was the dominant calendar in the western world, until it was superseded by the Gregorian calendar.
Leap year
The Julian calendar has 12 months, 365 days and a leap day added in February every four years giving an average year of 365,25 days.
Problem with the julian calendar
The actual average earth year is a few minutes shorter than 365,25 days meaning that the calendar gained about three days every four centuries.
The historical Julian calendar is currently 13 days advanced of the Gregorian calendar.
Gregorian calendar
I the western world we are following the Gregorian calendar[4] also called the Western or the Christian calendar. The Gregorian calendar is internationally the most widely accepted calendar and are used as civil calendar.
It was discovered that the actual average earth year was nearly 365,2425[5] days instead of the Julian 365,25 days, which lead to the calendar reform in the year 1582 introduced by Pope Gregory XIII[6].
Adoption of the Gregorian calendar
The Gregorian was adopted by various countries in different countries. For example Denmark adopted the Gregorian calender in year 1700[7] and the British Empire in year 1752.
When switching from the Julian to the Gregorian calendar it was necesarry to adjust the calender by dropping the the days accumulated in the nearly 1800 years since the Julian calender was introduced.
In the western world today we refer to the British adoption of the Gregorian calender 14th September 1752.