Mondo Knows Facts
Coordinated Universal Time replaced Greenwich Mean Time
The new standard relies on atomic clocks rather than the rotation of the Earth Greenwich Mean Time was defined by the Sun crossing the meridian at the observatory. Atomic clocks keep a far steadier second, and the two scales drift apart as Earth's spin slowly changes. Leap seconds were added to bridge the gap, though the practice is being phased out. It sits in Mondo's world geography collection, one of 200 facts that each trace back to the reference below.
Where this comes from
Facts that can change over time are reviewed and updated. If something here looks wrong, Mondo would rather know than be confidently incorrect.
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More facts like this
The 24-hour day comes from Earth's rotationThe division into 24 hours is ancient, but the length of the day is not perfectly constantTime zones follow politics more than the SunSeveral countries use offsets that sit far from their solar time, and some use half-hour stepsChina keeps one clock across five time zonesOfficial time in Beijing applies from the eastern coast to Xinjiang, nearly 5,000 kilometres westNepal's clock runs 45 minutes off the hourIts offset of five hours and 45 minutes is one of the oddest in the worldThe International Date Line is not a straight lineIt zigzags around countries so that no single state has to keep two calendar datesClocks are nudged to follow the spinning EarthSince 1972 the time signal has been stepped by a second now and then, because the planet does not keep perfect time
🗺️ World Geographyfact 184 of 200
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Tags: time-zones, clocks, standards
Coordinated Universal Time replaced Greenwich Mean Time: the short answers
- Where does this come from, and can I check it?
- The new standard relies on atomic clocks rather than the rotation of the Earth. The figure is taken from Royal Museums Greenwich, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.
- Is this really a world geography fact?
- Yes. It sits on the World Geography shelf, one of 2,600 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.
- What else can I read about it?
- The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.