I often envision a database in the sky that manages things like website addresses. Until today, I had not thought deeply about our need for a “clock in the sky.”
How did the world settle on “the time of day”? After all, until 1883, there were more than 300 local times in the United States. (Communities set clocks at noon based on when the sun was at its highest position in their sky.)
Ocean-going ships provided the impetus for invention.
Prior to the 18th century, time was, umm, fluid. Although Ancient Rome divided the year into eight-day weeks, the Babylonians and the Jewish people (Genesis) followed a seven-day week. In the fourth century, Constantine converted the Roman Empire to Christianity and the seven-day week followed.
Regardless of number of days in the week, sundials and water clocks had their own challenges for measuring time.
The clock emerged as a scientific instrument with the advent of Britain’s far-ranging Navy. Ship captains needed an accurate time keeper to determine longitude* when the shore is out of sight. (Latitude is a more straightforward measurement because the equator is a fixed location.)
The journey to GPS started in the late 17th century.
In 1675, King Charles II gifted Greenwich, a royal park and palace, for Britain’s first national observatory. British “mapmakers began to set longitude lines from Greenwich.”
Longitude lines show how distant a location is east or west of a universal vertical line, the Prime Meridian. It passes over the British Royal Observatory in Greenwich, England, from the North Pole to the South Pole.
The British parliament passed the Longitude Act in 1715 after a disaster illustrated the need to accurately calculate a ship’s position at sea. In 1765 (!), John Harrison won the Longitude Board contest set in place in 1715.
By the mid-19th century, the British rail system needed a national time system rather than deal with differing local times in towns and cities served by the railroad. There were no agreed upon timings “for when the day would begin and end” or the length of an hour.
On 02 August 1880, Parliament approved the “time as shown by the clocks at the Royal Observatory” as the nation’s official time. It’s name: Greenwich Mean Time.
Greenwich Mean Time or GMT is the time displayed by the Shepherd Gate Clock at the Royal Observatory in Greenwich, London. When the sun is at its highest point exactly above the Prime Meridian, it is 12:00 noon at Greenwich.
When days are measured by a clock, rather than by the sun, each day is equal to the average (mean) length of a solar day.
The US adopted GMT (and four time zones) on 18 November 1883.
Sir Sandford Fleming, a Canadian railway planner and engineer, proposed a standard worldwide time. In the late 19th century, “72% of the world’s commerce depended on sea-charts which used Greenwich as the Prime Meridian.”
And now we know what time it is, anywhere in the world! (Fast-forwarding through International Atomic Time and Coordinated Universal Time or UTC.)
* Longitude lines (meridians) are perpendicular to and latitude lines are parallel to the Equator.