Australia uses three main time zones: Australian Eastern Standard Time (AEST; UTC+10:00), Australian Central Standard Time (ACST; UTC+09:30) and Australian Western Standard Time (AWST; UTC+08:00).
Time is regulated by the individual state governments, some of which observe daylight saving time (DST). Daylight saving time (+1 hour) is used between the first Sunday in October and the first Sunday in April in jurisdictions in the south and south-east: New South Wales, Victoria, Tasmania, Jervis Bay Territory and the Australian Capital Territory switches to the Australian Eastern Daylight Saving Time (AEDT; UTC+11:00), and South Australia switches to the Australian Central Daylight Saving Time (ACDT; UTC+10:30).
Standard time was introduced in the 1890s when all of the Australian colonies adopted it. Before the switch to standard time zones, each local city or town was free to determine its local time, called local mean time. Now, Western Australia uses Western Standard Time; South Australia and the Northern Territory use Central Standard Time; while New South Wales, Queensland, Tasmania, Victoria, Jervis Bay Territory, and the Australian Capital Territory use Eastern Standard Time. Daylight saving time is not currently used in Western Australia, the Northern Territory or Queensland.
The Cocos (Keeling) Islands uses UTC+06:30 year round, Christmas Island uses UTC+07:00 year round, while Norfolk Island uses UTC+11:00 as standard time and UTC+12:00 as daylight saving time.
History
The standardisation of time in Australia began in 1892, when surveyors from the six colonies in Australia met in Melbourne for the Intercolonial Conference of Surveyors. The delegates accepted the recommendation of the 1884 International Meridian Conference to adopt Greenwich Mean Time (GMT) as the basis for standard time.
The colonies enacted time zone legislation, which took effect in February 1895. The clocks were set ahead of GMT by 8 hours in Western Australia; by 9 hours in South Australia (and the Northern Territory, which it governed); and by 10 hours in Queensland, New South Wales, Victoria, and Tasmania. The three time zones became known as Western Standard Time, Central Standard Time, and Eastern Standard Time. Broken Hill in the far west of New South Wales (strictly speaking, the county of Yancowinna) also adopted Central Standard Time due to it being connected at the time by rail to Adelaide but not Sydney.
In May 1899, in a break with the common international practice of setting one-hour intervals between adjacent time zones, South Australia advanced Central Standard Time by thirty minutes after lobbying by businesses who wanted to be closer to Melbourne time and cricketers and footballers who wanted more daylight to practice in the evenings. It also meant that South Australia became one of only a few places in the world which uses a time-zone meridian located outside of its geographical boundaries. Attempts to undo this change in 1986 and 1994 failed.
In 1911, when the Northern Territory was separated from South Australia and placed under the jurisdiction of the Federal Government, the Territory kept Central Standard Time. Likewise, when the ACT and Jervis Bay Territory were broken off from New South Wales, they retained Eastern Standard Time.
Since 1899, the only major changes in Australian time zones have been setting of clocks half an hour later than Eastern time (GMT plus 10:30) on the territory of Lord Howe Island, and Norfolk Island changing from UTC+11:30 to UTC+11:00 on 4 October 2015.
When abbreviating "Australian Central Time" and "Australian Eastern Time", in domestic contexts the leading "Australian" may be omitted; however, the prefix "A" is often used to avoid ambiguity with the time zone abbreviations "CST" and "EST" referring to the Central and Eastern Time Zones in North America.
Civil time and legislation
Though the governments of the states and territories have the power to legislate variations in time, the standard time within each of these is set related to Coordinated Universal Time (UTC) as determined by the International Bureau of Weights and Measures and set by section 8AA of the National Measurement Act of 1960 of the Commonwealth.