I Have just learnt after years of confusion that the main difference between the two terms The UK changes back to GMT in the winter. While the time in Greenwich may change to British Summer Time (BST) during the summer, actual GMT does not change with Daylight Savings Time. In reference to the comment about GMT and UTC differing in the summer for 7 months, this is inaccurate. 74.✗.✗.230įirst commenter is confusing GMT with British Summer Time, I think. Also, if you happen to have been born after the year 1990 chances are you are completely incapable of accurately reading a standard analog clock anyway, so you need not worry yourself with any of this time business - just check your phone and know someone smarter than you has paved the way for your ignorance. UTC is not a "time zone" at all - as is GMT. Some of the Facebook replies appear to be the direct result of heavy intoxication. Were it anything approximating a maximum of nine seconds, much confusion would ensue. Owing to the ambiguity of whether UTC or UT1 is meant, and because timekeeping laws usually refer to UTC, GMT is avoided in careful writing.Īctually the maximum permissible deviation between GMT amd UTC is 0.9 sec (i.e., nine tenths of one second) rather than 9 sec.(nine seconds). In casual use, Greenwich Mean Time (GMT) is the same as UTC and UT1. The difference between UTC and UT1 cannot exceed 0.9 s, so if high precision is not required, the general term Universal Time (without a suffix) may be used. Since unanimous agreement could not be achieved on using either the English word order, CUT ( coordinated universal time), or the French word order, TUC ( temps universel coordonné), the acronym UTC was chosen as a compromise. The ITU felt it was best to designate a single abbreviation for use in all languages in order to minimize confusion. Leap seconds are used to allow UTC to closely track UT1, which is the mean solar time at the Royal Observatory, Greenwich. UTC is the International Atomic Time (TAI, from the French Temps atomique international) with leap seconds added at irregular intervals to compensate for the Earth's slowing rotation. In 1970 the Coordinated Universal Time system was devised by an international advisory group of technical experts within the International Telecommunication Union (ITU). It is also used to refer to Universal Time (UT), which is an astronomical concept that directly replaced the original GMT. Strictly speaking, UTC is not a time zone but an atomic time scale which only approximates GMT in the old sense. It is now often used to refer to Coordinated Universal Time (UTC) when this is viewed as a time zone. Greenwich Mean Time (GMT) is a term originally referring to mean solar time at the Royal Observatory, Greenwich where a system was first developed around 1850 for tracking time based on the rotation of the Earth. Swatch even invented a concept called beat time that split each day into 1,000 beats on a decimal system, eradicating time zones entirely.įor those of you who don't operate on Internet Time, this spreadsheet shows the time zone in 195 countries, extracted from our World Factfiles series.Diffen › Science › Measurement › Measurement Units The development of the world wide web in the 1990s led to calls for a standardised internet time, as people in cyberspace were no longer bound by geography. Kiribati even extended its time zone 600 miles east in 1995, to include Caroline Island in the same zone (and, as it straddled the Date Line opposite the GMT meridian, the same date) as the country's other islands. Other time zones are counted to the east and west of this line, either plus or minus hours from GMT.Įach country sets its own time zone within this framework, so some zones extend beyond the meridian for convenience, while others, like India, take on half hours. The prime meridian, determined by the 1884 conference, runs through Greenwich, in the UK, giving us Greenwich Mean Time. The zones are based on 24 longitudinal meridian lines that run from the north to south poles. The Meridian Conference in 1884, attended by representatives from various countries, led to the creation of the 24 time zones we use today. Increasing globalisation in the Victorian era meant a need to standardise time zones, as businesses began to operate across wider areas and world travel became easier with the advent of the railway.
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