Coordinated Universal Time (UTC)
From Halbeeg, the open encyclopedia · Af-Soomaali
152 languages
Coordinated Universal Time, abbreviated internationally as UTC, is the primary time standard by which the world regulates clocks. Time zones in different regions are expressed as offsets from UTC—for example UTC+3 or UTC−5—indicating hours added to or subtracted from UTC.
UTC is based on atomic clocks, which measure time by counting the oscillations of cesium atoms. Because of this, UTC is highly precise compared to timekeeping methods that depend on Earth's rotation, which varies slightly.
Origins and name change
Before UTC, Greenwich Mean Time (GMT) was used, based on the solar observation meridian at the Greenwich line in London. UTC produces the same hour count as GMT, but the method of measurement differs: GMT depends on Earth's rotation, while UTC depends on atomic clocks and includes periodic adjustments.
Leap second adjustments
Because Earth's rotation gradually slows, UTC is occasionally extended by one additional second, known as a leap second. This step keeps UTC from drifting too far from solar time. International timekeeping authorities decide when to introduce leap seconds.
Present-day use
UTC serves as the standard for aviation, maritime operations, satellite communications, GPS systems, and computer networks. Most internet servers store time internally in UTC and convert to local time when displaying to users.