Telstra Research Laboratories
Leap Second - Video (1992)

About the video
TRL Cast
View the video (10_leapsec.mpg ~14Mb 01:20)
View the video (abc_leapsec.mpg ~6Mb 36 secs)

About the video

The rotation of the Earth on its axis and its rotation around the sun have served as the basis for timekeeping since the dawn of history. The day was divided into 24 hours, each of 60 minutes, each of 60 seconds. Over the centuries, the accuracy of time measurement has steadily improved and it was realised that there were irregularities in the Earth's rotation. In 1972 a new Coordinated Universal Time (UTC) scale was adopted by the scientific community for international use. It combines all the regularity of atomic time with most of the convenience of Greenwich Mean Time (GMT). The seconds of UTC are of the same length as those of TAI, and they occur at the same instants. UTC is kept always within one second of GMT by the insertion of extra seconds as necessary (positive leap seconds).

This insertion of extra seconds, still happens every 18 months and was done by TRL up to 3 or 4 years ago (1998). The leap second adjustment is carried out by programming one of the two time code generators to the new time scale (one second slow - for a positive leap second adjustment) and throwing the switch some time in advance to allow an automatic switchover to occur at the end of the 60th second of the last minute just prior to mid-night UTC. This usually corresponds to 11 am Australian Eastern Daylight Time (AEDT) on 1st January or 10 am Australian Eastern Standard Time (AEST) on the 1st July depending on when the leap second is declared. The result is that we have 61 seconds in the last minute just prior to 00 hours UTC. The decision for correcting time is taken by the International Earth Rotation Service (IERS), and notices are distributed well in advance whether or not a leap second is required. The Global Operations Centre (GOC) now run the Time and Frequency Standards which provide a time reference to Australia through the speaking clock service (1194) and its associated equipment which provide dial-up time via modem and hourly time signals to radio stations.

On this particular occasion, we have a capture from 2 of the evening news bulletins at the time that documented this event. The throwing of the switch captured in the videos was staged for the cameras as the actual leap second adjustment has to be critically timed and is handled by the equipment automatically.

Apologies for the quality but the source VHS tape was of a poor standard and thanks to Bruce Ratcliff for extra information provided.

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00:15 Bruce Ratcliff (Ch 10)

00:07 Bruce Ratcliff (Ch 2)

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Last updated: 14 May 2002