1 UTC Date Time System
1.1 UTC Time standard definition
Coordinated Universal Time (UTC) is the time standard by which the world regulates clocks and time.
The UTC is defined by an International Telecommunications Union recommendation and is based on International Atomic Time.
- the standard adopt leap seconds to adjust UTC Time and compensate for the slowing of Earth's rotation.
- Greenwich Mean Time (GMT) was formerly used as the international time standard, then UTC superseded GMT.
1.2 How UTC Time works
UTC divides time into days, hours, minutes and seconds.
UTC days
- are identified using the Gregorian calendar.
- contain 24 hours and each hour contains 60 minutes.
- almost all UTC days contain exactly 86,400 SI seconds.
UTC minutes:
- usually a minute contains 60 seconds, but (with an occasional leap second) a minute may contain 61 or 59.
- because of leap seconds, the minute and all larger time units are of variable duration.
UTC seconds:
- is the smaller time units of constant duration.
1.3 UTC Time Zones
Time zones are regions of the earth where the local time is defined as differing the UTC Time by an integer number of hours
- but some countries have established time zones that differ by a number of half-hours or quarter-hours from UTC.
- this difference or offset is positive or negative:
- the westernmost time zone is twelve hours behind UTC and is UTC-12
- the easternmost time zone is fourteen hours ahead of UTC and is UTC+14
Civil Time
Civil Time indicates the time designated by authorities or local time indicated by clocks.
- civil time is generally standard time in a time zone at a fixed offset from Coordinated Universal Time (UTC), adjusted by daylight saving time during part of the year.
The Civil Time in a particular time zone can be determined from the UTC Time by adding or subtracting the number of hours and minutes specified by the UTC offset.
1.4 Daylight Saving Time
UTC does not observe daylight saving time and does not change with seasons
Local Time or Civil Time may change if a time zone jurisdiction observes Daylight Saving Time (summer time).
Example:
- local time on the east coast of the United States is five hours behind UTC during winter, but four hours behind UTC during summer.
1.5 Who uses UTC
UTC is used by Computer systems and the Internet
- in the internet and World Wide Web standards
- the Network Time Protocol synchronizes the clocks of computers over the internet, using the UTC system
- email systems and other messaging systems time-stamp messages using UTC
- database records that include a time stamp use UTC
UTC is also the time standard used in aviation, weather forecasts, maps, amateur radio operators
