I have seen facts like "sometimes there is less than 60 seconds in a minute" With no explanation... Enjoy How long is a day? That depends. A day is a single rotation of the earth about its axis. It is never exactly twenty-four hours long. Astonishingly, it can be as much as fifty whole seconds longer or shorter. This is because the speed of the Earth’s rotation is continually changing as result of friction caused by tides, weather patterns and geological events. Over a year, an average day is a fraction of a second shorter than twenty-four hours. Once atomic clocks had recorded these discrepancies, the decision was made to redefine the second, hitherto a set fraction of the ‘solar’ day – i.e. an eighty-six-thousand-and-four-hundredth of a day. The new second was launched in 1967 and defined as: ‘the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.’ Accurate, but not easy to say when tired at the end of a long day. This new definition of a second means that the solar day is gradually drifting away from the atomic day. As a result, scientists have introduced a ‘leap second’ into the atomic year, to bring it into line with the solar year. The last ‘leap second’ added (the seventh since Coordinated Universal Time (UTC) was established in 1972) was on 31 December 2005, on the instruction of the International Earth Rotation Service based at the Paris Observatory. That’s good news for astronomers and those of us who want our watches to correspond to the movement of the Earth around the Sun, but bad news for computer software and all technology based on satellites. The idea was vigorously opposed by the International Telecommunication Union who made a formal proposal to abandon the leap second by December 2007. One compromise might be to wait until the discrepancy between UTC and GMT reaches an hour (in about 400 years time) and adjust it then. In the meantime, the debate about what constitutes the ‘real’ time continues.
Posted on: Thu, 15 Aug 2013 00:27:10 +0000
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