Time zones around the world are measured by referring to a specific point on the globe and calculating time from that point. This specific point is called the Greenwich Meridian. Occasionally this is called the Prime Meridan and it is located at the Royal Observatory in Greenwich, England.

Time is referred to as Greenwich Mean Time, although in recent years the more accurate title Coordinated Universal Time (abbreviated as UTC) is universally used. This time scale, UTC, uses an atomic time scale. UTC is utilized as a starting point to ascertain time in other countries though out the globe.
For example, if a country is stated as having the time UTC+3, this means that when it is noon in Greenwich, it is 3pm in that country.

Conversely, if a country is stated as having the time UTC-3, this means that when it is noon in Greenwich, it is 9am in that country.

Three Time Zones in Australia

Australia is a very big island and as such experiences three time zones. They are:

AEST – Australian Eastern Standard Time

ACST – Australian Central Standard Time; and

AWST – Australian Western Standard Time.

The three Australian Standard time zones are based on UTC, adjusted for longitude. The UTC calculations for the three time zones in Australia are:

AEST Australian Eastern Standard time = UTC + 10 hours (centred on 150⁰ East Longitude) and is used in Queensland, New South Wales, The Australian Capital Territory, Victoria and Tasmania.

ACST Australian Central Standard time = UTC + 9 ½ hours

AWST Australian Western Standard time = UTC + 8 hours


Daylight Saving Time

Daylight Saving Time is practiced in Australia but sometimes confusingly, not by all states at the same time. So I have listed each of the capital cities of Australia and noted the Daylight Saving time, when it is commenced and when it is ceased.

EDT Eastern Daylight Time UTC + 11 hours
EST Eastern Standard Time UTC + 10 hours
CDT Central Daylight Time UTC + 10:30 hours
CST Central Standard Time UTC + 9:30 hours
WDT Western Daylight Time UTC + 9 hours
WST Western Standard Time UTC + 8 hours

Sydney
UTC/GMT +10 hours (Eastern Standard Time EST)
Daylight savings in Sydney
starts: 2 October 2011
ends: 4 April 2012
starts: 7 October 2012
ends: 7 April 2013

Melbourne
UTC/GMT +10 hours (Eastern Standard Time EST)
Daylight savings in Melbourne
starts: 2 October 2011
ends: 4 April 2012
starts: 7 October 2012
ends: 7 April 2013

Adelaide
UTC/GMT +9:30 hours (Central Standard Time CST)
Daylight savings in Adelaide
starts: 2 October 2011
ends: 4 April 2012
starts: 7 October 2012
ends: 7 April 2013

Perth
UTC/GMT +8 hours (Western Standard Time WST)
There is no daylight saving in Western Australia

Darwin
UTC/GMT +9:30 hours (Central Standard Time CST)
There is no daylight saving in the Northern Territory.

Brisbane
UTC/GMT +10 hours (Eastern Standard Time EST)
There is no daylight saving in Queensland.

Canberra
UTC/GMT +10 hours (Eastern Standard Time EST)
Daylight saving in Canberra
starts: 2 October 2011
ends: 4 April 2012
starts: 7 October 2012
ends: 7 April 2013

Hobart
UTC/GMT +10 hours (Eastern Standard Time EST)
Daylight saving in Hobart
starts: 2 October 2011
ends: 4 April 2012
starts: 7 October 2012
ends: 7 April 2013