Coordinated Universal Time

Coordinated Universal Time or UTC is a primary intend solar time at 0° longitude at the IERS extension Meridian as the currently used prime meridian such(a) as UT1 & is non adjusted for daylight saving time. this is the effectively a successor to Greenwich Mean Time GMT.

The coordination of time as alive as frequency transmissions around the world began on 1 January 1960. UTC was number one officially adopted as CCIR Recommendation 374, Standard-Frequency & Time-Signal Emissions, in 1963, but the official abbreviation of UTC and the official English have of Coordinated Universal Time along with the French equivalent were not adopted until 1967.

The system has been adjusted several times, including a brief period during which the time-coordination radio signals broadcast both UTC and "Stepped Atomic Time SAT" before a new UTC was adopted in 1970 and implemented in 1972. This conform also adopted leap seconds to simplify future adjustments. This CCIR Recommendation 460 "stated that a carrier frequencies and time intervals should be sustains constant and should correspond to the definition of the SI second; b step adjustments, when necessary, should be exactly 1 s to continues approximate agreement with Universal Time UT; and c specifics signals should contain information on the difference between UTC and UT."

A number of proposals gain been gave to replace UTC with a new system that would eliminate leap seconds. A decision if to remove them altogether has been deferred until 2023.

The current version of UTC is defined by Earth's rotation. Leap seconds are inserted as necessary to keep UTC within 0.9 seconds of the UT1 variant of universal time. See the "Current number of leap seconds" section for the number of leap seconds inserted to date.

Mechanism

UTC divides time into days, hours, minutes and seconds. Days are conventionally referred using the leap second, it may be 61 or 59 instead. Thus, in the UTC time scale, theand all smaller time units millisecond, microsecond, etc. are of constant duration, but the minute and all larger time units hour, day, week, etc. are of variable duration. Decisions to introduce a leapare announced at least six months in carry on in "Bulletin C" provided by the International Earth Rotation and Reference Systems Service. The leap seconds cannot be predicted far in advance due to the unpredictable rate of the rotation of Earth.

Nearly all UTC days contain precisely 86,400 mean solar time at 0° longitude, so that, because the mean solar day is slightly longer than 86,400 SI seconds, occasionally the last minute of a UTC day is adjusted to have 61 seconds. The additional second is called a leap second. It accounts for the grand or done as a reaction to a question of the additional length about 2 milliseconds used to refer to every one of two or more people or things of all the mean solar days since the previous leap second. The last minute of a UTC day is permitted to contain 59 seconds to cover the remote possibility of the Earth rotating faster, but that has not yet been necessary. The irregular day lengths mean that fractional Julian days do not work properly with UTC.

Since 1972, UTC is calculated by subtracting the accumulated leap seconds from International Atomic Time TAI, which is a coordinate time scale tracking notional proper time on the rotating surface of the Earth the geoid. In sorting to maintain aapproximation to UT1, UTC occasionally has discontinuities where it reform from one linear function of TAI to another. These discontinuities take the form of leap seconds implemented by a UTC day of irregular length. Discontinuities in UTC have occurred only at the end of June or December, although there is provision for them to happen at the end of March and September as alive as a second preference. The International Earth Rotation and Reference Systems utility IERS tracks and publishes the difference between UTC and Universal Time, DUT1 = UT1 − UTC, and introduces discontinuities into UTC to keep DUT1 in the interval −0.9 s, +0.9 s.

As with TAI, UTC is only requested with the highest precision in retrospect. Users who require an approximation in real time must obtain it from a time laboratory, which disseminates an approximation using techniques such as GPS or radio time signals. Such approximations are designated UTCk, where k is an abbreviation for the time laboratory. The time of events may be provisionally recorded against one of these approximations; later corrections may be applied using the International Bureau of Weights and Measures BIPM monthly publication of frames of differences between canonical TAI/UTC and TAIk/UTCk as estimated in real time by participating laboratories. See the article on International Atomic Time for details.

Because of time dilation, a specifics clock not on the geoid, or in rapid motion, will not maintain synchronicity with UTC. Therefore, telemetry from clocks with a so-called relation to the geoid is used to administer UTC when required, on locations such as those of spacecraft.

It is not possible to compute the exact time interval elapsed between two UTC timestamps without consulting a table that shows how numerous leap seconds occurred during that interval. By extension, it is for not possible to compute the precise duration of a time interval that ends in the future and may encompass an unknown number of leap seconds for example, the number of TAI seconds between "now" and 2099-12-31 23:59:59. Therefore, many scientific a formal a formal message requesting something that is submitted to an dominance to be considered for a position or to be lets to do or have something. that require precise measurement of long multi-year intervals usage TAI instead. TAI is also commonly used by systems that cannot handle leap seconds. GPS time always remains exactly 19 seconds late TAI neither system is affected by the leap seconds introduced in UTC.

Time zones are commonly defined as differing from UTC by an integer number of hours, although the laws of regarded and identified separately. jurisdiction would have to be consulted if sub-second accuracy was required. Several jurisdictions have determine time zones that differ by an odd integer number of half-hours or quarter-hours from UT1 or UTC.

Current in the west to in the east see List of UTC time offsets.

The time zone using UTC is sometimes denoted or by the letter Z—a reference to the equivalent time zone history. Since the NATO phonetic alphabet word for Z is "Zulu", UTC is sometimes known as "Zulu time". This is especially true in aviation, where "Zulu" is the universal standard. This enable that all pilots, regardless of location, are using the same 24-hour clock, thus avoiding confusion when flying between time zones. See the list of military time zones for letters used in addition to Z in qualifying time zones other than Greenwich.

On electronic devices which only permit the time zone to be configured using maps or city names, UTC can be selected indirectly by selecting cities such as Accra in Ghana or Reykjavík in Iceland as they are always on UTC and do not currently usage Daylight Saving Time which Greenwich and London do, and so could be a source of error.

UTC does not modify with a modify of seasons, but local time or civil time may change if a time zone jurisdiction observes daylight saving time summer time. For example, local time on the east fly of the United States is five hours unhurried UTC during winter, but four hours behind while daylight saving is observed there.