loCAL |
Measure - The sun and the stars were our earliest timekeepers and, from ancient times until quite recently, most people used sundials as their most reliable clock. As the Earth rotates, the Sun seems to rise in the east and set in the west, reaching its highest point above the horizon at Noon. The Sun can only be directly 'above' one part of the Earth at a time, so Noon occurs at different moments from east to west. For example, in Norwich in the east of England Noon is five minutes ahead of London, while on Ben Nevis in the west of Scotland it is 20 minutes behind. Sundials can be accurate to within a few minutes at the place for which they were made.
Share - Public sundials were common in Europe in ancient times. After the invention of mechanical clock in the 13th century, public clocks were installed in churches and towers. These often used bells to sound the hours. The ringing bells created a shared time signal that enabled people to start work, eat and worship together. Use - Work in the fields has always been regulated by nature, but since the early middle ages break times were commonly set by the church bells. They sounded to indicate the time for group prayer at Noon and in the early evening. |
oBSERVATORY |
Measure - From the 17th century, the most advanced timekeepers have usually been found in observatories. By the 1700s, astronomers needed highly accurate clocks, called 'regulators', to chart the planets and stars for navigational purposes. They could also use their star observations to set the clocks themselves. As the weather changes, minute differences in atmospheric pressure can affect the timekeeping of the regulators. The mechanism of the regulator known as 'Dent 1906' was modified to over come this.
Share - As the need and desire for the 'right time' increased owners and makers of clocks and watches turned to observatories to provide accurate timekeeping. London watchmakers took their best timekeepers to the Royal Observatory to set them right. But travelling to Greenwich was not practical for everyone. The worlds leading observatories found ingenious ways of sharing daily time signals with their local communities, through cannon fire, dipping flags, telegraph arms and dropping time balls. Use - For astronomers, ships' navigators and clockmakers accurate time was very important in their trade. |
NATIONAL |
Measure - I the 18th and 19th centuries industrialisation changed the way people worked, travelled and communicated. Fast trains and the electric telegraph meant it was no longer practical for each city and town to keep its own local time. A single accurate time was needed across the country. This time had to be measured and distributed from one source. The time kept at the Royal Observatory - Greenwich Mean Time - became the national standard. The new telegraph network allowed GMT to be transmitted instantly around the world.
Share - Through the electrical telegraph networks, the time from the Shepherd Master clock at Greenwich was shared with the public through the simultaneous twitching, flicking and chiming of hundreds of time signals across the country. The Royal Observatory set up a Time Ball in 1833 to give a visual time signal. It still drops every day at 1:00 pm. By 1855, 98% of the nations clocks were set to Greenwich Mean Time, although GMT did not become the nation's legal standard until 1880 Use - The Industrial Revolution created a world regulated by time. An urban society needed a uniform time for travel, communications, work, appointments, events, administration and law. |
international |
Measure - By the 1880s, world trade, travel and communication demanded a global timekeeping system. An international conference in 1884 established the principle of 24 world 'time zones' based on the Greenwich Meridian. There was now an agreed method of comparing and sharing time, which was measured by a new generation of superbly accurate pendulum clocks. But it took several decades before the new system was accepted by all the countries of the world. Radio enabled time signals to be broadcast worldwide. In 1924, the BBC introduced its now famous 'six pip' sequence as a public time service.
Share - From the 1920s onwards, radio, telephone and mains electricity were all used to share accurate time. People have been able to call the 'speaking clock' on the telephone since 1936. The accurate time is always provided at the 'third stroke' or beep. Alongside the BBC's 'six pip' service, a separate, coded radio time signal was broadcast by the General Post Office from Rugby Radio Station from 1927 onwards. Enthusiasts and mariners were able to pick up the signal worldwide. The coded signal now controlled by the National Physical Laboratory is still broadcast today. Use - International business, financial markets, trade and communications rely on accurate, shared time keeping to synchronise and coordinate activity. Trading and sharing financial information continue around the clock. |
global |
Measure - Until the 1950s accurate time measurement was based on the apparent movement of the stars and planets. Today we put crystals and atoms at the heart of our precision timekeepers. When an electric current is passed through a quartz crystal it vibrates at a very precise frequency and creates a regular pulse for a clock mechanism. By the 1940s quartz clocks had replaced pendulum regulators in the world's observatories. Atomic clocks work by analysing the photons absorbed and emitted by caesium atoms. The next generation of atomic ion-trap clocks will be accurate to one second in billions of years.
Share - The worlds shared time is now a scale called 'Coordinated Universal Time' (UTC). 260 atomic clocks in 49 locations around the world send their data to the International Bureau of Weights and Measures (BIPM) in Paris, France. The BIPM calculates the master timescale and sends information back to each of the providers. We actually see this ultra-accurate time in our every day lives with computers, the internet, satellite broadcasting and mobile phones. It is also vital for satellite navigation systems such as the Global Positioning System (GPS). Use - Highly accurate is vital to key technologies that drive the modern world such as computers, the internet, satellites and mobile phones. |