The circuits were accurate enough to measure and record variations in the Earth’s rotation, but they were still limited in performance and sensitive to environmental changes. It kept time according to the mechanical resonance of vibrating crystals of piezoelectric material-which created electrical signals with a precise frequency. In the 1920s the quartz crystal oscillator circuit was invented. A BRIEF HISTORY OF TIMEKEEPINGįor thousands of years the reference for timekeeping was the Earth’s rotation rate-which was limited in accuracy. Administered by the IEEE History Center and supported by donors, the milestone program recognizes outstanding technical developments around the world. This month the atomic clock received an IEEE Milestone. The clock kept time by tracking the microwave signals that electrons in atoms emit when they change energy levels. The clock helped redefine the duration of a single second, and its groundbreaking accuracy contributed to technologies we rely on today, including cellphones and GPS receivers.īuilding on the accomplishments of previous researchers, Harold Lyons and his colleagues at the U.S. National Bureau of Standards (now the National Institute of Standards and Technology), in Washington, D.C., began working in 1947 on developing an atomic clock and demonstrated it to the public two years later. Today, Greenwich Mean Time (GMT) is only the name of a time zone that is used by a few countries in Africa and Western Europe, including the UK during winter and all year in Iceland.THE INSTITUTEThe invention of the atomic clock fundamentally altered the way that time is measured and kept. Since then, GMT is no longer a time standard.

Until 1972, Greenwich Mean Time (also known as Zulu time) was the same as Universal Time (UT). UTC was adjusted several times until 1972, when leap seconds were introduced to keep UTC in line with the Earth's rotation, which is not entirely even, and less exact than atomic clocks. The name Coordinated Universal Time was officially adopted in 1967. In 1960, the International Radio Consultative Committee formalized the concept of UTC, and it was put into practice the year after. The transit circle is a part of the telescope's mechanics and it is still cited as the prime meridian's original reference (0° longitude). The reference line or starting point, the Prime Meridian, was determined to be the transit circle at the Royal Observatory in Greenwich, London. This is the basis for the 24-hour time zone system we know today.Īt the time, Greenwich Mean Time (GMT) was chosen as the world’s time standard.

Universal Time (UT) was created at the International Meridian Conference in 1884. It is used to compare the pace provided by TAI with the actual length of a day on Earth.

Universal Time (UT1): Also known as astronomical time or solar time, it refers to the Earth's rotation.

International Atomic Time (TAI): A time scale that combines the output of some 400 highly precise atomic clocks worldwide, and provides the exact speed for our clocks to tick.

Two components are used to determine UTC: The world's timing centers have agreed to keep their time scales closely synchronized - or coordinated - therefore the name Coordinated Universal Time. UTC is the time standard commonly used across the world. ©/stocknshares A Standard, Not a Time Zone The Greenwich Meridian in London, England.

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