What is Time? The Standardisation of Time

The adoption of a single time standard in 1884 brought timekeeping into a new era of simultaneous communication.

(This is the ninth post of Time and Clocks, the thread that follows Time and Calendars.)

The Greenwich Observatory

The Royal Observatory at Greenwich, London was established in 1675 by King Charles II and from those first years it has remained a world authority on matters of astronomy, navigation and timekeeping. The observatory gathered astronomical data and measurements of the earth’s rotation, providing information essential for navigation and communication. Throughout the whole of the eighteenth century, it played a central role in encouraging and testing the developments of accurate measurements for navigation at sea with the chase for the great Longitude Prize.

London, Greenwich, Royal Greenwich Observatory; The Shepherd 24-hour Gate Clock is one of the earliest electrically driven public clocks and was installed here in 1852. The dial always shows Greenwich Mean Time (GMT). Being 24-hour clock, the hour hand marks noon at the bottom of the dial and midnight at the top. The time shown is accurate to 0.5 of a second.

The Observatory consolidated its authority in the nineteenth century. As the Industrial Revolution swept through Britain, the construction of the railway from the 1830s represented a major advance in communication and trade: the introduction of railway timetables revealed the potential for chaos as the impact of the 30-minute time difference between Land’s End and Lowestoft was realised. In 1880 England, Scotland and Wales agreed to use a single standard of time, governed by master clocks at Greenwich, adopting the Greenwich Mean Time. The new electric telegraph, another major advance of the Industrial Revolution, was used to distribute a time signal from a master pendulum clock to time signals around the country.

The Radio Pips and Beyond

The distribution of the time standards was in a perpetual state of refinement so that by the early 1920s and the coming of radio, a great opportunity was seized for a universal audible confirmation of the correct time. The successor to the original six pips is still being transmitted every hour on BBC Radio 4 and the World Service. In the USA, a similar service was established by the US equivalent of Greenwich, National Institute of Standards and Technology (NIST), which also transmitted signals and messages on the telephone. The signals were accurate to within one thousandth of a second when corrected for distance from the receiver.

By 1975 signals were distributed to the whole of the western hemisphere via satellites above the equator, with two weather satellites broadcasting a time code accurate to within 100 microseconds. The United States Naval Observatory (USNO), established in 1830 as the Depot of Charts and Instruments to care for the US Navy’s chronometers and charts, is now the de facto manager of precision time: a system of caesium clocks and hydrogen maser clocks constructs a time reference point which produces signals to make the USNO master clock. This master clock is used in a time server which can be dialled into on the Internet or can be received by a radio-controlled watch. Both Britain and France have similar time systems and together they form part of an international network which controls our standards of time.

Yes this is a clock, at least, an array of caesium beam atomic clocks, the US Naval Observatory (USNO) Alternate Master Clock at Schriever Air Force Base, Colorado. It contributes to the international atomic time standard UTC.

Universal Time

In 1972, an agreement was reached to manage the difference between the time standard based on the earth’s rotational time (GMT) and the new atomic standards based on the oscillations of caesium which were independent of the earth and its astronomical motion. This new standard was called Co-ordinated Universal Time (its acronym, UTC, is a typical political compromise because the French and the English both wanted to use the initials from their own respective language): under this system, caesium time is held until nearly one second difference appears with GMT, then a leap second is inserted. The International Bureau of Weights and Measures in Paris receives data from observatories around the world and co-ordinates the necessary changes.

Time Zones

Time zones became necessary in the USA by the 1860s, because trains could travel hundreds of miles in a day. Until then people relied on local time, which changed one minute for every 12 miles travelled in an east-west direction in mid-America. This gave over 300 local times for a journey across the USA, so 100 train zones were established.

In 1883, the USA was divided into four time zones based on the 75th, 90th, 105th and 120th meridians. At noon on 13 November 1883, the electric telegraph distributed GMT to all the major cities, so that the local authorities could adjust their clocks to their new zone’s time.

In 1884 the International Meridian Conference in Washington DC established world zones with 24 standard meridians every 15 degrees east and west of 0 at Greenwich, as centres of the zones. The International Dateline, the passage from one day to the next, was drawn on 180 meridian in the Pacific, the frantic zigzag of the international dateline reflecting the desire of islands and nations such as Fiji, Kiribati and Samoa not to be split.