{"id":64414,"date":"2022-08-19T00:19:16","date_gmt":"2022-08-19T04:19:16","guid":{"rendered":"https:\/\/world.edu\/?p=64414"},"modified":"2022-08-19T00:19:16","modified_gmt":"2022-08-19T04:19:16","slug":"days-on-earth-have-mysteriously-gotten-longer-and-scientists-dont-yet-know-why","status":"publish","type":"post","link":"https:\/\/world.edu\/days-on-earth-have-mysteriously-gotten-longer-and-scientists-dont-yet-know-why\/","title":{"rendered":"Days on Earth have mysteriously gotten longer, and scientists don’t (yet) know why"},"content":{"rendered":"

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\nAtomic clocks<\/a> combined with precise astronomical measurements have recently revealed that the length of a day on Earth is suddenly getting longer . This phenomenon has critical implications not only for our measurement of time, but also for things like GPS and other technologies that govern our modern lives.<\/p>\n

In recent decades, the rotation of the Earth around its axis, which determines the length of a day, has accelerated. This trend has shortened our days; in fact, in June 2022 we hit the record shortest day<\/a> in about half a century.<\/p>\n

But despite this record, since 2020, this constant acceleration has curiously turned into a slowdown: the days are getting longer again, and the reason remains unknown for the moment.<\/p>\n

While our phone clocks show that a day has exactly 24 hours, the actual time it takes for the Earth to complete a single rotation varies very slightly. These changes occur over periods ranging from millions of years to almost instantaneously \u2013 even earthquakes and storms can play a role. So it turns out that a day very rarely corresponds to the magic number of 86,400 seconds.<\/p>\n

The ever-changing planet<\/strong>
\nFor millions of years, the rotation of the Earth has slowed down due to the frictional effects associated with the tides caused by the Moon. This process adds about 2.3 milliseconds to the length of each day each century. A few billion years ago, an Earth day lasted only 19 hours<\/a> .<\/p>\n

Over the past 20,000 years, another process has worked in reverse, accelerating the Earth’s rotation. At the end of the last ice age, the melting of the polar ice caps<\/a> reduced the pressure on the surface, and the Earth’s mantle began to move steadily towards the poles.<\/p>\n

Just as a ballet dancer spins faster when he brings his arms closer to his body \u2013 the axis around which he spins \u2013 so our planet’s rotation speed increases when this mass of mantle gets closer to the axis of Earth. And this process is shortening each day by about 0.6 milliseconds per century.<\/p>\n

Over decades and longer, the connection between the Earth’s interior and surface also comes into play. Large earthquakes can change the length of the day, although normally by small amounts. For example, the 2011 Great T\u014dhoku earthquake <\/a>in Japan, with a magnitude of 8.9, is said to have accelerated the Earth’s rotation by a relatively small 1.8 microsecond<\/a>s .<\/p>\n

Apart from these large-scale changes, over shorter time periods, weather and climate also have large impacts on the Earth’s rotation, causing variations in both directions.<\/p>\n

Bimonthly and monthly tidal cycles move mass around the planet, causing changes in day length of up to a millisecond in either direction. We can observe tidal variations<\/a> in daylength records for periods of up to 18.6 years. The movement of our atmosphere has a particularly strong effect, and ocean currents also play a role. Snow cover and seasonal precipitation, or groundwater extraction, further alter things.<\/p>\n

Why is the Earth suddenly slowing down?<\/strong>
\nSince the 1960s, when operators of radio telescopes around the planet began devising techniques to simultaneously observe<\/a> cosmic objects like quasars , we have had very accurate estimates of Earth’s rotational speed.
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