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Astronomers found that written records of solar eclipses in ancient China and the Middle East did not match astronomical models \u2013 until the Earth\u2019s slowing rotation was factored in. (Wikimedia Commons: Kalan, CC BY 3.0<\/a>)<\/p>\n But over shorter time periods, our planet occasionally spins faster.<\/p>\n Since about 2020, Earth has sped up.<\/p>\n University of Tasmania geodesist Lucia McCallum said several things could affect the Earth’s spin.<\/p>\n “Atmosphere, wind, big ocean currents, glaciers melting, big volcanoes, redistribution of mass in the inner Earth,” Dr McCallum said.<\/p>\n This slight variation means the traditional definition of a second is not precise enough for technologies such as GPS, which needs to measure fractions of milliseconds to work.<\/p>\n Atomic time more precise<\/p>\n In the late 1960s, the governing body of the International Bureau of Weights and Measures (BIPM), which standardises the world’s measurements, adopted a more precise definition of a second based on measurements of caesium atoms.<\/p>\n This is what underpins coordinated universal time (UTC).<\/p>\n UTC is tracked by atomic clocks, currently the most accurate measures of time, although newer “nuclear clocks<\/a>” may soon surpass them.<\/p>\n The National Measurement Institute maintains atomic clocks, which are the most accurate methods of keeping time. (Supplied: National Measurement Institute)<\/p>\n Australia’s National Measurement Institute (NMI) leader of time standards, Michael Wouters, said the atomic second was as close to the traditional second as possible.<\/p>\n “There was no exact value to begin with because it was changing all the time,” he said.<\/p>\n Dr McCallum helps measure the speed of Earth’s rotation using telescopes pointed at extremely distant black holes.<\/p>\n “We use those black holes as anchor points,” Dr McCallum said.<\/p>\n Radio telescopes, like this one at Hobart’s Mt Pleasant Observatory, can observe an ultra-distant black hole and compare their signals to establish how quickly the Earth is spinning. (Supplied: Jim Lovell)<\/p>\n These observations are vital for satellite navigation, and they are also used to tell when the Earth’s rotation falls out of sync with UTC, prompting a leap second.<\/p>\n Since their introduction in 1972, leap seconds have been added to our clocks 27 times, most recently at the end of 2016.<\/p>\n How leap seconds mess with modern life<\/p>\n Leap seconds have become increasingly difficult to deal with in the computer age.<\/p>\n University of Technology Sydney computer networking researcher Darryl Veitch said leap seconds broke some software’s assumptions about time, such as that it only moved forwards and there were 60 seconds in a minute.<\/p>\n But Dr Wouters said people “forgot about this problem, and they wrote software that then crashed when time went backwards”.<\/p>\n Several things slow down the Earth’s rotation, but the influence of the Moon and tides is a major factor. (Supplied: NASA)<\/p>\n Unlike time zones or daylight saving, leap seconds are irregular, scheduled only six months in advance.<\/p>\n Previously, they have caused platforms, including internet technology provider Cloudflare and social media site Reddit, to crash.<\/p>\n In 2022, the BIPM’s governing body decided to abandon the leap second by 2035<\/a> and start discussing a different method of keeping Earth’s days in sync with UTC.<\/p>\n But the decision needed to be fast-tracked when Earth started speeding up because it meant the next leap second might need to be “negative”.<\/p>\n Increasingly interconnected systems mean that a timekeeping error in one place can snowball. (Unsplash: Lukas Blazek)<\/p>\n Dr Wouters said a negative leap second was less likely to cause problems because it involved time jumping forwards rather than backwards, but Professor Veitch was not so sure.<\/p>\n “It’s never happened before, and therefore the software for that has never been tested,” Professor Veitch said.<\/p>\n Since leap seconds will soon be retired, introducing a negative one seems an unnecessary risk.<\/p>\n “It’s being cautious about an unusual event that’s prompting the accelerated timetable,” Dr Wouters said.<\/p>\n Nor are there any clear economic or practical arguments for preserving leap seconds, beyond keeping software engineers busy.<\/p>\n “Some people have a philosophical objection to [losing leap seconds], and that’s because we’re disconnecting the way we count time from our actual experience of it,” Dr Wouters said.<\/p>\n “But clocks themselves are a very artificial thing.”Vote may create ‘leap hour’<\/p>\n The governing body of the BIPM will vote on leap seconds at its meeting on 12 \u201315 October.<\/p>\n The leading proposal is to let UTC drift from Earth’s rotation until it is an hour out of sync, and then observe a “leap hour” to bring it back.<\/p>\n Ceasing leap seconds means that Earth’s day and night will slowly fall out of sync with official time, but it will take more than a century for a minute of difference to build up. (ESO: Anton Yankovyi, CC BY 4.40<\/a>)<\/p>\n Earth’s rotation currently loses less than a second per year, so it could take more than a millennium for this leap hour to become necessary.<\/p>\n Our current timekeeping systems are less than a century old, and it is likely they will look very different by then.<\/p>\n “I would imagine in 100 years, software would be completely automated, and we just won’t have the kinds of problems we have now,” Professor Veitch said.<\/p>\n![\"Large](\"https:\/\/www.newsbeep.com\/au\/wp-content\/uploads\/2026\/10\/1791781093_899_58addd854ae470559afd14aad96db598.jpeg\")
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