Explanation of the Standard Time Act 2009
The Standard Time Act 2009 (the Act) repealed the former Standard Time Act 1898 and replaced it with updated legislation that reflects the internationally accepted time standard.
The Act replaced references to Greenwich Mean Time with a more accurate time measurement scale called Co-ordinated Universal Time.
Co-ordinated Universal Time is an international time scale recommended by the International Bureau of Weights and Measures as the legal basis for time. It is a method of measuring time using atomic clocks. Greenwich Mean Time, which is based on astronomical observations, is an average (mean) because the actual time taken for the Earth's rotation varies slightly from day to day. Measurements taken by atomic clocks vary far less.
The Commonwealth National Measurements Act 1960 was amended in 1997 to provide that Co-ordinated Universal Time is the time scale to be maintained by Australia's Chief Metrologist. Following a recommendation from the National Time Commission (now National Measurement Institute) in 2004, the Standing Committee of Attorneys-General agreed that each State and Territory would adopt Co-ordinated Universal Time as the basis for calculating the passage of time.
Since that recommendation all other jurisdictions have made appropriate amendments to their standard time legislation. The enactment of this Act ensures that South Australia operates as part of a uniform national time standard.
The Act does not change the actual time in South Australia to any noticeable degree. The difference between Greenwich Mean Time and Co-ordinated Universal Time is measured in fractions of a second. Moreover, whenever the cumulative difference approaches one second, an adjustment is made in Co-ordinated Universal Time to reduce the gap.
The difference is important, however, in some scientific matters. For example, it is relevant in computer programmes that use high speed data transfers and in universal synchronisation matters. It is also the basis of the satellite global positioning system.
To determine the international standard of Co-ordinated Universal Time, the Bureau of Weights and Measures in Paris coordinates data from atomic clocks located in timing laboratories around the globe, including at the Australian National Measurement Institute.
The Act sets South Australian standard time 9 hours and 30 minutes ahead of Coordinated Universal Time. The previous Act (1898) similarly set the time in this State by reference to the meridian of longitude 142.5 degrees east of Greenwich Mean Time, which equated to 9.5 hours (every 15 degrees equals 1 hour).
The Act fundamentally relates to the measurement of the passage of time and is not about the time zoning of South Australia. It has no relationship with the adoption of Eastern Standard Time or True Central Standard Time, nor any change to or discontinuance of Daylight Saving Time.
The Act has no practical effect on the general community. The public and businesses that rely upon precise time measurement, however, will benefit from the certainty in the use of uniform terminology in standard time legislation throughout Australia.