The Standard of Years - Era Epoch
In ancient China, emperors would set year names to record the year. For example, Zhenguan was the year name set by Emperor Taizong of Tang Dynasty, so the world used the first year of Zhenguan and the second year of Zhenguan to record the year. Emperors can change their reign names for various reasons. For example, Wu Zetian used 17 reign names during her 21-year reign. Obviously, it is bound to be very difficult for us to calculate how many years have passed since the first year of Shenlong. But, fortunately, we used the way of the AD calendar later.
AD, namely the Gregorian calendar era, is an internationally accepted calendar system.
This calendar system takes the legendary birth year of Jesus Christ as the first year of the Gregorian calendar, which is equivalent to the first year of Emperor Ping of the Western Han Dynasty in China.
A.D
- AD , also written as AD AD, Anno Domini, is an abbreviation of anno Domini nostri Jesu Christi, meaning the Year of Jesus Christ
- BC , BC, Before Christ, means before Christ
standard of time
Regarding the standard of time, there are also some concepts:
- IAT: International Atomic Time, atomic time, is a time standard obtained by atomic clocks.
Atomic clocks are the most accurate time measurement and frequency standards known in the world, with an error of less than 1 second in 37 years.
It can be understood as a very accurate timekeeping instrument, similar to a clock. - UT: Universal Time, world time. A time standard based on the rotation of the Earth. There are several standards for universal time, differing from each other by at most a few seconds. The most commonly used are UTC and UT1.
- UTC, Coordinated Universal Time. based on atomic time seconds
- GMT, Greenwich Mean Time, based on the Earth's rotation
- CST , Beijing time China Standard Time
UTC
The phrase for Universal Coordinated Time in French is Temps Universel Coordonne, abbreviated as TUC; the phrase in English is Universal Coordinated Time, abbreviated as UCT. The two do not give in to each other, and finally coordinate and use UTC.
UTC, known as the time standard time, is directly translated from the above English/published text, and is also known as the International Coordinated Time.
UTC is based on the length of atomic hours and seconds, and is a time measurement system that is as close as possible to time. Widely used in Internet and World Wide Web standards.
ＧＭＴ
GMT, Greenwich Mean Time, also known as Greenwich Mean Time or Greenwich Mean Time, was originally translated as Greenwich Mean Time.
GMT, Greenwich Mean Time, Greenwich Mean Time, is the standard time of the Greenwich Observatory located in the suburbs of London.
- The prime meridian is defined as the line of longitude passing through
- Noon in GMT is the time when the sun crosses the Greenwich meridian.
Due to the uneven movement speed of the earth's orbit, the daily rotation of the earth is irregular and is slowly decelerating. Therefore, GMT time is no longer used as the standard time, but GMT, which uses atomic clocks to tell the time.
UTC and GMT relationship
- UTC is the most scientific and accurate
- GMT is equivalent to UTC when accuracy to the second is not required.
- CST Beijing time, East Eighth District, ahead of standard time by 8 hours.
GMT+08:00
Origin of time zone
Time Zone, time zone, when the International Conference on Longitude was held in Washington in 1884, in order to overcome the global time confusion, the world was divided into 24 time zones. China adopts the time of the East Eighth District, where the capital Beijing is located, as the national unified time, that is, Beijing time.
- At that meeting, it was stipulated that Greenwich, London, England should be the starting point of the zero-degree meridian. Because the earth rotates 360 degrees every 24 hours from west to east, there is a difference of one hour every 15 degrees.
- Time zone difference, positive in the east and negative in the west, Beijing time east eighth district, +8
time zone division is as follows:
some time zones
- China Stanard Time , CST China Standard Time UTC+8 UT+8:00
- Central Standard Time(USA) UT-6:00 American Standard Time
- Central Standard Time(Australia) UT+9:30 Australian Standard Time
- Cuba Standard Time UT-4:00 Cuba Standard Time
What is a timestamp?
Timestamp: UTC counts seconds from 0:00:00 on January 1, 1970, and this number of seconds is a timestamp. That is, how many seconds have elapsed from that time to the specified time.
The total number of seconds from January 1, 1970 (00:00:00 GMT) to the current time, also known as the Unix timestamp.
Why does the timestamp start from 1970?
The UNIX operating system agrees on January 1, 1970 as the time epoch, that is, the start time.
The initial operating system is 32-bit, and the timestamp is represented by an integer, 2^31 -1 = 2147483647 The
total number of seconds in a year = 365 24 60*60 = 31536000
The value divided by the two is 68.1
32-bit representation of events The maximum interval is 68 years. Considering the era of computer generation, take January 1, 1970 as the era of UNIX system time. Java also follows this convention.
After the 64-bit operating system appeared, there was no such problem.
Representation of time - ISO8601:2000
- 4 digits for year, 2 digits for month, 2 digits for day
- The year consists of 4 digits, AD 1 is 0001, now is 2021, BC is 0000
- Time representation: hours, minutes and seconds are 2 digits. Add a capital letter Z at the end of UTC, and other time zones are represented by time + time difference.
14:30:05Z22:30:05+08:00
- The combination of date + time means: Add a capital letter T in front of the time.
2021-05-03T17:30:08+08:00