Irish Standard Time

Ireland uses Irish Standard Time (IST, UTC+01:00; Irish: Am Caighdeánach Éireannach) in the summer months and Greenwich Mean Time (UTC+0) in the winter period.

In Ireland, the Standard Time Act 1968 legally established that the time for general purposes in the State (to be known as standard time) shall be one hour in advance of Greenwich mean time throughout the year. This act was amended by the Standard Time (Amendment) Act 1971, which legally established Greenwich Mean Time as a winter time period. Ireland therefore operates one hour behind standard time during the winter period, and reverts to standard time in the summer months. This is defined in contrast to the other states in the European Union, which operate one hour ahead of standard time during the summer period, but produces the same end result.

The instant of transition to and from daylight saving time is synchronised across Europe. In Ireland, Winter time begins at 02:00 IST on the last Sunday in October (changing to 01:00 GMT), and ends at 01:00 GMT on the last Sunday in March (changing to 02:00 IST).

The following table lists recent past and near-future starting and ending dates of Irish Standard Time:

Before 1880, the legal time at any place in the United Kingdom of Great Britain and Ireland was defined as local mean time, as held by the appeal in the 1858 court case Curtis v. March. The Statutes (Definition of Time) Act, 1880 defined Dublin Mean Time as the legal time for Ireland. This was the local mean time at Dunsink Observatory outside Dublin, and was about 25 minutes 21 seconds behind Greenwich Mean Time (GMT), which was defined by the same act to be the legal time for Great Britain. After the Easter Rising, the time difference between Ireland and Britain was found inconvenient for telegraphic communication and the Time (Ireland) Act, 1916 provided that Irish time would be the same as British time, from 2:00 am Dublin Mean Time on Sunday 1 October 1916. Summer time (daylight saving time) had been introduced in May 1916 across the United Kingdom as a temporary efficiency measure for the First World War, and the changeover from Dublin time to Greenwich time was simultaneous with the changeover from summer time to winter time.John Dillon opposed the first reading of the Time (Ireland) Bill for having been introduced without consultation of the Irish Parliamentary Party; he said the different time in Ireland "reminds us that we are coming into a strange country".T. M. Healy opposed the second reading on the basis that "while the Daylight Saving Bill added to the length of your daylight, this Bill adds to the length of your darkness".

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