Difference Between GMT and UTC
UT is Greenwich Mean Time whereas UTC is Coordinated Universal Time. UT refers to the time kept at the Royal Observatory in Greenwich, London, called mean solar time. UTC is based on International Atomic Time (TAI).
The Greenwich Time is based on astronomical observations, it is used primarily by the bodies involved in the UK as the BBC World Service, the Royal Navy and the Met Office. International Bureau of Weights and Measures (BIPM) have recommended Coordinated Universal Time (UTC) as the legal basis for the time. It is a method to measure time using atomic clocks. To determine the international standard of Coordinated Universal Time, the Bureau of Weights and Measures (BIPM) in Paris coordinates data set of atomic clocks positioned in timing laboratories around the globe. It is interesting to note that leap seconds are added to UTC to compensate for the retarding rotation of the Earth.
It is important to know that leap seconds are used to allow UTC to track the mean solar time at the Royal Observatory in Greenwich, London.
In fact many countries are adopting GMT in their legislation. They are the United Kingdom, Belgium, the Republic of Ireland and Canada. UTC is the second time standard used for quite a few Internet and World Wide Web standards. It is also the basis of the global positioning system (GPS). UTC is used as the Network Time Protocol, designed to synchronize the clocks of many computers on the Internet. Greenwich Mean Time and Coordinated Universal Time differ by fractions of a second. This difference matters in scientific calculations.
Thus we can say that the UTC is the time standard based Internet while TU is the country based standard time. In casual use when fractions of a second are considered not very important, GMT can be considered equivalent to UTC. It is often believed that the time zones around the world are positive or negative offsets from UTC. In fact is quite true UTC replaced GMT as the time scale of the main reference in the different regions.
The International Telecommunication Union otherwise called ITU thought it was best to have a single abbreviation for use in all languages so that the confusion can be reduced to a large extent. In fact they could not reach a conclusion whether to have the word order of English or French word order and therefore now the acronym UTC was chosen.