Portal:Time/Selected Article archive

Selected article May 2008

Chip-scale atomic clock unveiled by NIST

An atomic clock is a type of clock that uses an atomic resonance frequency standard to feed its counter. Early atomic clocks were masers with attached equipment. Today's best atomic frequency standards (or clocks) are based on absorption spectroscopy of cold atoms in atomic fountains. National standards agencies maintain an accuracy of 10^-9 seconds per day (approximately 1 part in 10¹⁴), and a precision set by the radio transmitter pumping the maser. The clocks maintain a continuous and stable time scale, International Atomic Time (TAI).

Recently selected: Atomic clock

Selected article June 2008

The first quartz clock, on display at the International Watchmaking Museum, in La Chaux-de-Fonds, Switzerland

The history of timekeeping devices encompasses the various methods used to measure time throughout history.

The origins of the current Western time measurement system date to approximately 2000 BC, in Sumer. The system developed then—which remains in use today—was sexagesimal. The Ancient Egyptians classified day and night as each being twelve hours long... Water clocks, called clepsydras by the Greeks, were also of early Egyptian design, probably first used in the Precinct of Amun-Re; their use continued, especially in Greece. Around this period, the Chinese, ruled by the Shang dynasty, are thought to have used the outflow water clock, which was introduced from Mesopotamia as early as 2000 BC. Other ancient timekeeping devices include the candle clock, used in China, Japan, and England; the timestick, used in India and Tibet, as well as some parts of Europe; and hourglasses, which functioned similarly to a water clock.

Recently selected: Atomic clock - History of timekeeping devices