Greenwich Mean Time (GMT) is a term originally referring to mean solar time at the Royal Observatory in Greenwich, London. It is commonly used in practice to refer to Coordinated Universal Time (UTC) when this is viewed as a time zone, especially by bodies connected with the United Kingdom, such as the BBC World Service, the Royal Navy, the Met Office and others, although strictly UTC is an atomic time scale which only approximates GMT with a tolerance of 0.9 second.
A time zone is a region of the earth that has uniform standard time, usually referred to as the local time. By convention, time zones compute their local time as an offset from UTC. Local time is UTC plus the current time zone offset for the considered location.
The Prime Meridian is the meridian at which the longitude is defined to be 0°. The Prime Meridian and its opposite the 180th meridian (at 180° longitude), which the International Date Line generally follows, form a great circle that divides the Earth into the Eastern and Western Hemispheres.
Western European Summer Time (WEST) is a summer daylight saving time scheme, 1 hour ahead of Coordinated Universal Time. It is used in the following places: the Canary Islands the Faroe Islands Ireland the Crown dependencies the Madeira islands Continental Portugal the United Kingdom Western European Summer Time is also known by other names: British Summer Time (BST) in the United Kingdom. Irish Standard Time (IST) (Am Caighdeánach na hÉireann) in Ireland.
Japan Standard Time or JST is the standard timezone of Japan, and is 9 hours ahead of UTC. For example, when it is midnight in UTC, it is 9 am in Japan Standard Time. There is no daylight saving time, though its introduction has been debated several times. Japan Standard Time is the same as Korea Standard Time, Eastern Indonesia Standard Time and Yakutsk Time. During World War II, it was often called Tokyo Standard Time in Western contexts.
Korea Standard Time is the standard time zone in North and South Korea and is 9 hours ahead of UTC: i.e. , when it is midnight UTC, it is 9 am Korea Standard Time. Korea does not currently observe daylight saving time but has experimented with it in the past. Korea Standard Time is the same as Japan Standard Time, Indonesian Eastern Standard Time and Yakutsk Time.
The Durand Line refers to the border between Afghanistan and Pakistan, which is poorly marked and approximately 2,640 kilometers (1,610 miles) long. It was established after the 1893 Durand Line Agreement between the Government of colonial British India and Afghan Amir Abdur Rahman Khan for fixing the limit of their respective spheres of influence. It is named after Henry Mortimer Durand, the Foreign Secretary of British India at the time.
The International Date Line (IDL) is an imaginary line on the surface of the Earth opposite the Prime Meridian where the date changes as one travels east or west across it. Roughly along 180° longitude, with diversions to pass around some territories and island groups, it mostly corresponds to the time zone boundary separating −12 and +12 hours Coordinated Universal Time (UTC).
The Central Time Zone is in the Americas and observes standard time by subtracting six hours from UTC during standard time (UTC–6) and five hours during daylight saving time (UTC–5). The clock time in this zone, composed almost totally of a strip of territory in North America, is based on the mean solar time of the 90th meridian west of the Greenwich Observatory. In the United States and Canada, this time zone is generically called Central Time (CT).
The Eastern Time Zone (ET) of the Western Hemisphere – also known as North American Eastern Standard Time (NAEST) – is a time zone that falls mostly along the east coast of North America and the west coast of South America. Its UTC time offset is −5 hrs during standard time and -4 hrs during daylight saving time. The clock time in this zone is based on the mean solar time of the 75th meridian west of the Greenwich Observatory.