European Summer Time
Encyclopedia
European Summer Time is the arrangement in Europe by which clocks are advanced by one hour in spring to make the most of seasonal daylight. This is done in all of the countries of Europe except Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...

 which observes Greenwich Mean Time
Greenwich Mean Time
Greenwich Mean Time is a term originally referring to mean solar time at the Royal Observatory in Greenwich, London. It is arguably the same as Coordinated Universal Time and when this is viewed as a time zone the name Greenwich Mean Time is especially used by bodies connected with the United...

 (GMT) all year round, and Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

, which has two time zones in Europe: Kaliningrad Oblast
Kaliningrad Oblast
Kaliningrad Oblast is a federal subject of Russia situated on the Baltic coast. It has a population of The oblast forms the westernmost part of the Russian Federation, but it has no land connection to the rest of Russia. Since its creation it has been an exclave of the Russian SFSR and then the...

, which observes Kaliningrad Time
Kaliningrad Time
Further-eastern European Time is since September 2011 defined as three hours ahead of UTC...

, (UTC+03:00), and the rest of European Russia
European Russia
European Russia refers to the western areas of Russia that lie within Europe, comprising roughly 3,960,000 square kilometres , larger in area than India, and spanning across 40% of Europe. Its eastern border is defined by the Ural Mountains and in the south it is defined by the border with...

, which observes Moscow Time
Moscow Time
Moscow Time is the time zone for the city of Moscow, Russia and most of western Russia, including Saint Petersburg. It is the second westernmost of the nine time zones of Russia. Moscow Time has been UTC+4 year-round since 27 March 2011....

, (UTC+04:00).

The period extends from 01:00 UTC on the last Sunday in March until 01:00 UTC on the last Sunday in October each year. Europe is currently observing Summer Time.

History

Historically the countries of Europe had different practices for observing summer time, but this hindered coordination of transport, communications and movements. However by the 1980s with international flights becoming common the European Community began issuing directives requiring member states to legislate particular start and end dates for summer-time.

Since 1981 each directive has specified a transition time of 01:00 UTC and a start date of the last Sunday in March, but the end dates have differed. In 1981 and 1982 the end dates were the fourth Sunday in October. In 1983 the end date was changed to the last Sunday in September for all time zones other than Western European Time
Western European Time
Western European Time , defined legally as Greenwich Mean Time in the United Kingdom, is the time zone covering parts of western and northwestern Europe, and includes the following countries and regions:...

. In 1996 the end date for all time zones was changed to the fourth Sunday in October. In 1998 the end date was adjusted to be the last Sunday in October; this happened to be the same as the previous rule for 1996 and 1997. The ninth directive, currently in force, has made this permanent.

Exact timing for the next several years

European Summer Time begins (clocks go forward) at 01:00 UTC on/4 + 4) mod 7}} March +1)/4 + 4) mod 7}} March +2)/4 + 4) mod 7}} March +3)/4 + 4) mod 7}} March

Formula used to calculate the beginning of European Summer Time:

Sunday (31 − ((((5 * y) ÷ 4) + 4) mod 7)) March at 01:00 GMT

(valid until 2099), where y is the year, and for the nonnegative a, a mod
Modulo operation
In computing, the modulo operation finds the remainder of division of one number by another.Given two positive numbers, and , a modulo n can be thought of as the remainder, on division of a by n...

 b is the remainder
Remainder
In arithmetic, the remainder is the amount "left over" after the division of two integers which cannot be expressed with an integer quotient....

 of division after truncating both operands to an integer.

European Summer Time ends (clocks go backward) at 01:00 GMT on/4 + 1) mod 7}} October +1)/4 + 1) mod 7}} October +2)/4 + 1) mod 7}} October +3)/4 + 1) mod 7}} October

Formula used to calculate the end of European Summer Time:

Sunday (31 − ((((5 * y) ÷ 4) + 1) mod 7)) October at 01:00 GMT

(validity as above).

Local observations

In most of Europe the word Summer is added to the name of each European time zone
Time zone
A time zone is a region on Earth that has a uniform standard time for legal, commercial, and social purposes. In order for the same clock time to always correspond to the same portion of the day as the Earth rotates , different places on the Earth need to have different clock times...

 during this period: thus, in the UTC+01:00 time zone, Central European Time
Central European Time
Central European Time , used in most parts of the European Union, is a standard time that is 1 hour ahead of Coordinated Universal Time . The time offset from UTC can be written as +01:00...

 becomes Central European Summer Time
Central European Summer Time
Central European Summer Time is one of the names of the Daylight saving time offset using the UTC offset of UTC+02:00, 2 hours ahead of Coordinated Universal Time. It is used as a summer daylight saving time in most European countries. During the winter, Central European Time is used...

 (UTC+02:00).

In the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 local time during this period is known as British Summer Time
British Summer Time
Western European Summer Time is a summer daylight saving time scheme, 1 hour ahead of Coordinated Universal Time. It is used in the following places:* the Canary Islands* Portugal * Ireland...

 (BST) while local time during the rest of the year is normally referred to as Greenwich Mean Time.

In Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

, local time during this period is known as "IST", which officially stands for "Irish Standard Time", not "Irish Summer Time". Ireland's official timezone is CET (UTC+1), but this only applies during the summer (when areas in Europe that use CET are in CEST), with clocks being moved back one hour for winter time (known variously in the country as WET, UTC or GMT).

Western Europe

All parts of Western and Central Europe (except Iceland) whether or not in the EU, use the EU rules for both the date and the time of their clock changes.

Russia & Belarus

Until it ceased observing daylight saving time in 2011, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

 and Belarus
Belarus
Belarus , officially the Republic of Belarus, is a landlocked country in Eastern Europe, bordered clockwise by Russia to the northeast, Ukraine to the south, Poland to the west, and Lithuania and Latvia to the northwest. Its capital is Minsk; other major cities include Brest, Grodno , Gomel ,...

 observed Summer Time and make the change forward and back on the same dates as the European Union (respectively, on the last Sunday in March and the last Sunday in October) – with the difference, that the changeover on both dates took place in RU & BY not at 01:00 UTC as in the rest of Europe, but at 02:00 local time (03:00 local daylight-saving time in October) in each time zone.

Turkey

Turkey observes the EU rules for both the date and the time of its clock changes.

For the year 2011, Turkey switched to European Summer Time at 3:00 am in the night from Sunday March 27 to Monday March 28, one day later than the rest of Europe, to avoid disrupting the
examination for admission to higher education (YGS) held nation-wide on March 27.
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