|BoxMatrix >> Lexicon >> Internationalisation >> UTC||@|
|Short for:||Universal Time, Coordinated|
|Location:||Lexicon >> Internationalisation|
|Description:||Reference time and base of all Timezones|
Coordinated Universal Time), successor of GMT (
Greenwich Mean Time), is the base Timezone for the world.
Since 1972 all Timezones of this planet are relative offsets to the UTC which is based on the IRM prime meridian (0° longit.).
Before GMT was used which is based on a slightly differing meridian. Today GMT is a Timezone which is defined UTC+0.
This sounds more trivial than it is. Our time and date system is definied as:
- 1 minute = 59 - 61 seconds (60 +- Leap-Second)
- 1 hour = 60 minutes
- 1 day = 24 hours
- 1 month = 28 - 31 days
- 1 year = 12 months = 365 - 366 days (366 only in a Leap-Year)
For long time a reference second was derived from a caesium atomic clock, and a day being 60 x 60 x 24 = 86400 seconds.
But a day should also narrow a rotation of the earth, which is not as precise as this definition and changes with time.
That is why the concept of Leap-Seconds has been added to keep the daylight in sync with the time definition.
Besides this a month should narrow the revolution of the moon around the earth (27.32 days average) or better the visible
moon phases which additionally depend on the revolution of the earth around the sun (together 29.53 days average).
That's why the 12 months have differing amount of days to keep the calendar in sync with the moon phases.
And finally a year should narrow the revolution of the earth around the sun (365.256 days average).
This extra quarter of a day is compensated by adding the 29th of february each Leap-Year, which occurs each 4 years.
You see the mechanics of our sun / earth / moon orbits and spins are not as precise as our need to have an exact base time
and date. The systems to handle these offsets are still in permanent discussion and will surely evolve.
See the Timezone article.