GMT - is an acronym and it refers to Greenwich Mean Time, which is actually a time zone, one out of 24 time zones. GMT is the solar time, given at a certain moment in the Royal Observatory in Greenwich, UK. This time zone was the main reference for time keeping. It is located on zero degrees longitude and it passes right throughout the Royal Observatory in London (Greenwich Observatory). The time zones were defined and established in accordance with the GMT. In 1850, the first system for time tracking was actually developed at the Greenwich Royal Observatory. GMT is equivalent UTC for UK.

UTC - is an acronym for Coordinated Universal Time, which refers to a time standard designed and adopted for regulating time and clock. This is the basis for time and time zones all around the world. UTC does not refer to a local time and no country use it in such a way. UTC is not a time zone rather a concept, anatomic time scale. UTC is actually a zero longitude, based on atomic time. This time standard became the world’s official time standard in 1972. The noon is defined by 12:00, whereas the clock at midnight is 0:00. This was not the case before 1928 because according to GMT, those years the day starts at noon which was marked with 0:00.

UTC is a standard for time keeping, which and when Earth is slowing its rotation seconds are added, referred as a leap seconds. To be more precise, ax extra second is called a leap second because a solar day is longer than 86.400 seconds. As we know, the Earth has an elliptical form and uneven speed. Digital synchronized clocks found in observatories use UTC that is measured by atomic transition principle.

GMT system is based on the solar time, the Earth’s rotation. It is used by human readable clocks and is measured by the rotation of the Earth. On the other hand, digital synchronized clocks found in observatories use UTC that is measured by atomic transition principle.

The main difference between the GMT and UTC is that the first one is a time zone whereas the second one is a widely accepted standard for clock and time keeping. UTC is mainly used worldwide in aviation, air traffic control, international space station, and weather forecast. GMT is used in the countries that belong to this time zone, mainly UK, Iceland and some African countries. Moreover, during the summer months UK does not obey to the GMT time zone, the British Summer time zone is used instead. In case you want to check the real time, refer to Iceland. The country uses the GMT time zone but the daylight saving time does not apply. Another different between UTC and GMT is that UTC never changes whereas the GMT time changes when the daylight saving time is applied.