Time and date 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
Calendar standards
In the western world we are using the Gregorian calender which is a solar calendar following the seasons and the Earth's orbit around the Sun
- See the article Calendar standards
Clock and Time standards
The clock are used to describe the time of the day and follows the Earth's rotation around itself. Each day representing one rotation of the Earth.
- See the article Clock and Time standards
Computer time and date
A specific time includes a date and a clock time describing a specific Earth rotation around the Sun and specific Earth rotation around itself. The Earth's rotation around the Sun are influenced by it's elliptical orbit. The Earth rotation around itself called a solar day[1] are slowly decreasing increasing the length of the day.
The length of a day
Defined in ISO 8601 the day consists of 24 hours consisting of 60 minutes of 60 seconds. giving a total of <math>24 * 60 * 60 = 86400 seconds</math> a day. With the Earth rotation slowing down there are two possible ways to make the clock time match the rotation of the Earth.
- Decreasing the length of the second to match 86400 second/day
- Introducing a leap second[2] when needed.