![]() ![]() Leap seconds are inserted as necessary to keep UTC within 0.9 seconds of the UT1 variant of universal time. The current version of UTC is defined by International Telecommunication Union Recommendation (ITU-R TF.460-6), Standard-frequency and time-signal emissions, and is based on International Atomic Time (TAI) with leap seconds added at irregular intervals to compensate for the accumulated difference between TAI and time measured by Earth's rotation. ![]() The General Conference on Weights and Measures adopted a resolution to alter UTC with a new system that would eliminate leap seconds by 2035. This CCIR Recommendation 460 "stated that (a) carrier frequencies and time intervals should be maintained constant and should correspond to the definition of the SI second (b) step adjustments, when necessary, should be exactly 1 s to maintain approximate agreement with Universal Time (UT) and (c) standard signals should contain information on the difference between UTC and UT." This change also adopted leap seconds to simplify future adjustments. 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. UTC was first officially adopted as CCIR Recommendation 374, Standard-Frequency and Time-Signal Emissions, in 1963, but the official abbreviation of UTC and the official English name of Coordinated Universal Time (along with the French equivalent) were not adopted until 1967. The coordination of time and frequency transmissions around the world began on 1 January 1960. It is effectively a successor to Greenwich Mean Time (GMT). It is within about one second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used prime meridian) and is not adjusted for daylight saving time. One of the main reasons why Greenwich was chosen rather than Paris as the prime meridian was because its antipode does not traverse any land.Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. The International Date Line is on the opposite side of the Earth to the Greenwich meridian. Japan is the only industrialised country not to use it. During certain periods of the year, generally from April to September in the northern hemisphere and from October to March in the southern hemisphere, one hour is added. Civil time is the time in force within a country. These intercalary seconds are added at the initiative of the International Earth Rotation Service to ensure that, on average over the years, the sun is over the Greenwich meridian at 12:00:00 UTC to within nine-tenths of a second. UTC is itself derived from International Atomic Time (TAI) from which it differs only by a whole number of seconds, currently 32. UTC is the legal basis of time in the world. By international convention, UTC is equivalent to GMT, however their measurements differ: GMT is measured from midday, whereas UTC is measured from midnight. On 1st January 1982, following a decision by the International Telecommunication Union (UIT), GMT was replaced by UTC (Coordinated Universal Time), in order to correct universal time, in which the duration of the day is not constant throughout the year due to the Earth’s rotation on its axis. China for example has adopted a single time for its entire territory, while India encompasses a time difference of five and a half hours. However, time-zones follow national frontiers and some countries depart from universal time. The GMT system was adopted internationally on 1st January 1885. GMT is the mean solar time calculated at midday. Since one day lasts 24 hours, the terrestrial globe is “divided” into 24 zones whose longitude differs by 15° (one hour), with the middle of each zone dictating the time in the latter. This meridian was also used to determine time-zones, and original time or GMT (Greenwich Mean Time). Greenwich, located in the south-east suburbs of London, was until 1946 home to the Royal Observatory of the same name. After some tough discussions, particularly between the French and the British, the Washington international conference in October 1884 adopted the Greenwich meridian as the prime meridian for measuring longitude.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |