UTC (Coordinated Universal Time)
utc
The primary time standard by which the world regulates clocks and time, serving as the basis for civil timekeeping globally.
Atomic Clock
atomic clock
Overview
An atomic clock measures time by detecting the electromagnetic radiation emitted or absorbed when electrons transition between energy levels in an atom. Because the frequency is set by the atom itself, every clock built to the same design reproduces the same universal reference no matter where it stands. Gravity, magnetic and electric fields, motion, temperature, and blackbody radiation from the surroundings all shift that frequency slightly, so clocks in service measure those shifts and correct for them. Since 1967 the SI second has been defined as exactly 9,192,631,770 oscillations of the cesium-133 hyperfine transition.
Main Types
Cesium atomic clocks are the most widely deployed standard; cesium fountain clocks achieve an accuracy of about one second in 300 million years. Rubidium clocks are smaller and cheaper, making them practical for GPS satellites, where they fly alongside onboard cesium units, and they offer excellent short-term stability though less long-term accuracy than cesium. Hydrogen masers offer the best short-term stability and are used in VLBI observations and deep-space communications. Optical lattice clocks represent the next generation, reaching one second in 30 billion years and are candidates for redefining the SI second.
Applications
Atomic clocks underpin GPS satellite positioning (each satellite carries onboard clocks), telecommunications network synchronization, financial-transaction timestamps, and precision scientific measurements. If optical lattice clocks reach full practical deployment, their sensitivity to gravitational potential differences could enable "relativistic geodesy" for underground resource exploration and volcanic activity monitoring.
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