The 'six-pip' master clock at the Royal Observatory, Greenwich, used for the BBC 'six-pip' time signal from 1924. Photo: Paul Lauener
By Paul Lauener
London, Oct 27 (Docklands Wire) – When, twice a year, clocks in Britain shift between British Summer Time and Greenwich Mean Time, many people are blissfully aware of why this happens.
The job of knowing why the clocks change and what GMT actually is falls to David Rooney, the Curator of Time at the Royal Observatory in Greenwich.
He is a historical guardian of time. His job is “to preserve and share the memory of time,” by conveying the history and the science of time to the observatory’s million visitors a year.
Rooney has been fascinated with time since his father started a clock making business from the family home.
“I grew up with the sound of ticking clocks and striking and chiming,” he said.
Rooney works in what he describes as “the home of time,” Greenwich, the G in GMT, which a global conference decided 125 years ago should be the starting point for time.
Greenwich was chosen because the vast majority of ships already on the water used charts based on the Greenwich Meridian, making Greenwich the line which officially divides the Eastern and Western Hemisphere.
Anything either side of this ‘prime meridian’ was divided into 24 time zones, each representing an hour of the day.
CHANGING TIME
Ever since this decision was made, politicians and world leaders have been debating what time it should be in their country and many changes have been made.
At least 39 time zones are now in use worldwide, with some based on half-hour and 45 minute differences.
Earlier this month, the British-ruled Channel Island of Jersey held a referendum on whether to abandon GMT for the Central European Time of Paris and Berlin in order to gain an extra hour of business. A large majority opted to stay with GMT.
“It’s only one of many attempts over the last few years to change time,” said Rooney.
In Venezuela, President Hugo Chavez is in the process of moving its time zone forward by one half-hour and in China the whole country runs on Beijing time, despite the fact that China straddles five time zones.
In Britain, legislators have submitted several bills to parliament to change time to GMT +1 hour in the winter, and GMT + 2 hours in the summer to give UK residents lighter evenings, essentially shifting the UK to Central European Time under another name.
“There’s always been these attempts to shift time,” said Rooney. “Time has always been a political tool.”
Those who begrudge rising an hour earlier in the summer have a South London builder, William Willet, to thank. He used to ride his horse through London early in the morning and was incensed by what he saw as a waste of sunshine, pushing a bill through parliament to move the clocks forward an hour in summer and creating BST, British Summer Time.
HIDDEN INFRASTRUCTURE OF TIME
The Royal Observatory is no longer responsible for measuring GMT. An average is taken from a consortium of 260 atomic clocks by a laboratory in France.
The latest atomic clock is so accurate that if it had been set running at the start of the universe 13 billion years ago it would be half a second out today.
This new time standard is known as Coordinated Universal Time, or UTC, the time which people now get when they phone Britain’s speaking clock, which still receives 80 million calls a year, is UTC.
This marks a dramatic shift as day to day time is no longer measured by the Earth’s relationship to the sun. If UTC was left unchanged it would gradually drift away from the natural day-and-night cycle by a few fractions of a second per year.
To make up for this, the International Earth Rotation Service (IERS) continues to measure GMT. If UTC drifts more than 9/10 of a second from GMT, the IERS instructs the world’s 260 atomic clocks to insert a leap second.
This is either done on June 30 or Dec 31 at midnight. The public can hear this happen by listening to the BBC’s Time Signal, which adds an extra pip to the normal six pips it emits at midnight.
“You might think it’s because you’ve had too much to drink but in fact it’s that the world has added an extra second,” said Rooney, who describes his role as the guardian of time as his dream job.
He does, however, admit that the job has its pressures.
“It’s a nightmare if I’m late for work. The boss doesn’t like that at all.”
