The world is the earliest time standard.
In 1884, the international 1s was defined as the 1/8.64x104 of the daily average length of the year. The time system formed by this standard, called the World, is UT1.
The International atomic timescale began to be used internationally in 1972, and since then, the time Meridian by the Greenwich Old observatory has been called the world, the UT2,
or Greenwich Mean Time (GMT), is the world when the periodic difference of the Earth's rotational speed is corrected.
TAI-International Atomic Time
International Atomic Time
At the 13th session of the International Conference on Weights and Measures in 1967, a resolution was adopted to define the duration of the 9,192,631,770-week transition period of two super fine energy levels between the 133 ground state of the CS-atom, which was characterized by the extremely regular oscillation period of the cesium atom.
The time used is the international atom defined in the October 1971, which is compared with about 200 atomic clocks in the world and then processed by the time of the International Bureau of Weights and Measures, and then the unified atom is obtained.
GMT-Greenwich Mean Time, average Greenwich time
Greenwich Mean Time
Since the Earth's orbit is not circular, its operating speed changes with the distance between the Earth and the sun, so it lacks uniformity to see the sun.
The length of the sun day is also affected by the tilt of the Earth's rotation axis relative to the orbital plane.
To correct the above heterogeneity, astronomers calculate the effect of the Earth's non-circular trajectory and polar axis tilting to the sun.
When the sun is flat, it refers to the revised view of the sun. The flat sun on the Greenwich meridian is called the World Time (UT0), also known as Greenwich (GMT).
UTC-coordinated World time
Universal Time coordinated
UTC is developed and recommended by the International Radio Advisory Board, which is equivalent to the average sun time on the meridian (longitude 0 degrees).
It is the time after the average sun (GMT in Greenwich Mean Time), the new time mark after the Earth's motion is corrected, and the international atoms in "seconds",
The computational process is fairly rigorous, so UTC is more accurate than GMT in terms of "world standard Time".
The error value must remain within 0.9 seconds, and if greater than 0.9 seconds is released by the International Earth Rotation transaction NCBs in Paris, the UTC will be the same as the Earth rotation cycle.
So essentially the nature of UTC emphasizes a more precise world time standard than GMT. It's actually a more precise GMT.
Time in your time zone. The conversion relationship between UTC or GMT and LT is as follows: lt=utc+ time zone difference;
The east side is a corresponding time zone difference, and the west side is minus the time zone difference. If Beijing is the East eight district, then Beijing time =utc+
We generally think that GMT and UTC are the same as the local time in London, England.
For a simple example, the time zone in XP is GMT and the time zone in Win7 is UTC
Reprint Address: http://www.cnblogs.com/LubinLew/p/Knownledge_Time.html