GMT Time Zone

History of GMT Time Zone

It was decided that the solar time at the Royal Observatory, Greenwich would be the perfect location to define the Universal day, due to its longitudinal location. Due to Greenwich's location on the Earth, the Greenwich Meridian is part of the Earth's prime meridian, which is a line of longitude at which the longitude is at which longitude is defined as 0°.

The Greenwich Mean Time Zone applies in the United Kingdom and the Republic of Ireland, as well as Portugal, Iceland, Morocco, and several other countries. The biggest city in this time zone is London, the capital of England and the United Kingdom, which has a population of around 8.8 million people throughout its Greater London area, and 14 million in its entire metropolitan area. Other major cities in this time zone include Dublin, Lisbon, and Casablanca, which are each the largest cities in their respective nations.

• Why did British mariners use Greenwich Mean Time (GMT)?
  • The United Kingdom is a maritime nation, surrounded by seas and oceans.
  • British mariners used GMT as a navigational aid.
  • They would compare the time on their ships with a chronometer set to GMT to determine their longitudinal position.
• When was Greenwich Mean Time adopted in the United Kingdom?
  • Greenwich Mean Time was adopted across the United Kingdom in 1847.
  • It was introduced to help railway companies provide more accurate timings and schedules for their trains.
• Where did the Greenwich Mean Time Zone expand to?
  • The GMT zone later expanded to the Channel Islands of Jersey and Guernsey.
  • Ireland also adopted GMT in 1916.
• Did other countries use Greenwich Mean Time?
  • Several other countries adopted GMT over the years, though some later switched to different time zones.
  • France observed GMT from 1911 but switched to GMT+1 in 1940, using GMT+2 in the summer.
  • Spain also observed GMT until 1940, when the Spanish dictator Francisco Franco decided to abandon the system.

Details of the GMT Time Zone

An interesting fact about the Greenwich Mean Time Zone is that the location on which the zone is based, Greenwich, doesn't actually observe GMT all-year long. This is because the United Kingdom moves into British Summer Time, or BST, which begins on the last Sunday of March and runs through until the final Sunday of October each year. BST is GMT+1 or UTC+1 and was established via the Summer Time Act of 1916.

• Which countries observe Greenwich Mean Time (GMT) in winter?
  • GMT, which is effectively the same as Coordinated Universal Time (UTC), is observed in several countries and territories during the winter months of the Northern Hemisphere.
  • These areas include:
  • United Kingdom
  • Republic of Ireland
  • Portugal
  • Morocco
  • Western Sahara
  • During the summer months, these regions switch to UTC+1 due to daylight saving time.
• Which countries and territories observe GMT year-round?
  • Several locations follow GMT all year long as they do not implement daylight saving time:
  • Iceland
  • Ivory Coast
  • Ghana
  • Guinea
  • The Gambia
  • Burkina Faso
  • Guinea-Bissau
  • Liberia
  • Mali
  • Mauritania
  • Senegal
  • Sierra Leone
  • Togo
  • Faroe Islands
  • Canary Islands (Spain)
  • British Overseas Territory of Saint Helena, Ascension, and Tristan da Cunha
• Which locations observe GMT only in summer?
  • Two locations observe GMT only during the summer of the Northern Hemisphere:
  • A small part of eastern Greenland around the community of Ittoqqortoormiit.
  • The Autonomous Region of the Azores (Portugal).
  • These areas normally follow UTC-1 but move their clocks forward one hour in the summer to observe GMT/UTC.
• What are the westernmost and easternmost points where GMT is used?
  • The westernmost point where GMT is used is on the smallest of the Canary Islands at 18°00' W.
  • The easternmost point where GMT is used is in the United Kingdom, in the coastal town of Lowestoft, East Anglia.