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A question of time and tide

23 January 2012

The solar year is measured between two March equinoxes and has a duration of 365.2422 days. The Gregorian calendar, which is universally adopted throughout the world, is 365 days in length. So, unless a correction is made, our time keeping would gradually lose step with the seasons - hence we have a leap year every four years, and that extra day at the end of February on which, woe betide, you happen to be born, as your subsequent birthday celebrations become quadrennial rather than annual.

This year happens to be a leap year, but it is also a year when that other, rather more fleeting global time adjustment - the leap second – came under close scrutiny, as representatives from countries all over the world gathered at the International Telecommunications Union's (ITU’s) Radiocommunication Assembly (RA-12) in Geneva last week to discuss Co-ordinated Universal Time (UTC). This is a time reference administered in Paris and is based upon measurements submitted by the global network of atomic clocks.

The 'leap second' – that extra second that is added to, or taken away from, the time scale every few years to synchronise atomic clocks with the Earth's somewhat erratic period of rotation - was first implemented in 1972, allowing Earth rotation time to be recovered from broadcast values of UTC for celestial navigation purposes.

Current telecommunications, GPS navigation systems and even time-stamped financial transactions utilise continuous timing to the nearest nanosecond for their data transmissions and there has been some pressure from these sectors to modify the definition of UTC to a continuous time scale, free from inconvenient and unpredictable one-second step changes. A key item on the RA-12 agenda included a vote to decide whether or not to abolish the leap second. But the 70% consensus needed to achieve this was not forthcoming and a decision on the leap second has now been deferred until the ITU meets to discuss it again in 2015.

Some countries have supported the abolition of leap seconds on the grounds that technologies such as satellite navigation systems and communications networks require an extremely stable continuous time scale to operate correctly. Leap seconds have to be added manually, as it cannot accurately be predicted when they are needed. This is inconvenient and introduces the potential for error, which might be dangerous where mission critical systems are concerned.

However, the removal of leap seconds will mean that the atomic time scale will gradually drift apart from the solar time scale. This will take a long time; it will be about 50 years before the difference reaches a minute - and several hundred years before it reaches an hour - but eventually some adjustment will be needed to ensure that the two time scales do not diverge to an unacceptable degree. This might involve the introduction of  ‘leap minutes’ or even ‘leap hours’ at some distant future date

The UK government position is that UTC with leap seconds provides a viable basis for civil timekeeping worldwide and there is no urgent need to change its definition. Science minister, David Willetts believes we should stick to the current system. “Without leap seconds we will eventually lose the link between time and people's everyday experience of day and night," he says, now likely breathing a sigh of relief that the world’s time reference – Greenwich Mean Time – stays put in South East London and is unlikely to move to Paris for the foreseeable future.

The next leap second is due to be added on June 30 2012.

IMechE counts its 100,000th member
Are the surge in applications for engineering degrees and a historic milestone for one of the UK’s oldest engineering institutions signs of a much-needed resurgence of the profession? The 164 year old Institution of Mechanical Engineers has appointed its 100,000th member - County Antrim engineer Nicola McClatchey - and chief executive Stephen Tetlow wasted no time to exclaim the significance of this milestone.

“The country of Brunel, Stephenson and Whittle is witnessing a much-needed resurgence in engineering,” he says. “It is more popular among British students than ever and the growth of engineering-based industries, such as UK car manufacturing, is proving to be one of the few bright spots in an otherwise gloomy economic backdrop.”

An analysis of UCAS figures by the Institution shows a surge in applicants to engineering subjects since the 2008 financial crisis. There was a 35% rise in prospective students choosing engineering subjects in 2010 from 2007 levels, with mechanical engineering the most popular engineering discipline. More students are now choosing engineering than law, languages or teaching.

With annual tuition fees rising to £9,000 this year, it is not surprising to see a slight dip in current engineering applications (-1.8%) for 2012. This is still well short of the average dip in university applications (-6%) this year, so should we be encouraged that a long term decline may at last have been checked?

Les Hunt

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