[NTD, Beijing time, August 1, 2022]It takes 24 hours for the earth to rotate once, right? Almost but not entirely accurate. On Friday (July 29), the Earth’s rotation was the fastest on record, 1.59 milliseconds less than its standard 24 hours (86,400 seconds).
The length of the day is currently “slightly” shorter than the normal 24 hours due to the acceleration of Earth’s rotation, according to a report from Live Science. The 28 fastest days on record since 2005 are all in 2020. In 2020, Earth is spinning a few milliseconds faster than its average speed.
July 19, 2020, set a record for the shortest day, which was 1.47 milliseconds shorter than the standard 24-hour day. Before that, the shortest day occurred on July 5, 2005, 1.0516 milliseconds shorter than the standard 24-hour day.
In 2021, Earth continues to spin at a generally increasing rate, but it doesn’t break any records. However, scientists predict that a 50-year short-day phase may have already begun.
The reason for the different rotational speeds of the Earth remains a mystery. But scientists speculate that this could be due to the movement of the lava inside the Earth, the weight loss at the poles due to melting glaciers, seismic activity, changes in the oceans, tides, and even climate, or the “Chandler wobble,” or the Earth’s rotation. Small movements of an axis relative to the Earth’s surface.
Two systems of time measurement are currently used around the world: Scientists at the International Earth Rotation Service (IERS) determine the exact speed at which the Earth is rotating by measuring the precise moment at which a fixed star passes a certain location in the sky each day. This measurement is called Universal Time (UT1), a type of solar time.
The other is the International Atomic Time (TAI) determined by atomic clock data provided by more than 70 punctuality laboratories around the world. As time goes on, the time difference between Universal Time UT1 and Atomic Time TAI on the two time scales will become larger and larger. In order to solve this contradiction, UTC came into being.
The UTC second length adopts the atomic time second length, and the difference between UTC and UT1 is kept within ±0.9 seconds, otherwise UTC is adjusted by 1 whole second. This whole second is called a leap second.
Earth’s faster rotation could lead to the introduction of negative leap seconds to keep Earth’s orbit around the sun in line with atomic clock measurements.
Leap seconds have their advantages and disadvantages, and are useful for ensuring that astronomical observations are synchronized with clock time, but for some data-logging applications and telecommunications infrastructure, they can be a nuisance. It will have potentially confusing consequences for smartphones, computers and communication systems.
Leap seconds are “primarily beneficial to scientists and astronomers,” but it’s a “risky practice that does more harm than good,” according to the Meta blog. A positive leap second would cause the clock to run from 23:59:59 to 23:59:60 instead of resetting to 00:00:00. Time jumps like this can crash the program and corrupt the data due to the timestamp of the data store.
Meta also said that in the event of a negative leap second, the clock would go from 23:59:58 to 00:00:00, which could have “disruptive effects” on software that relies on timers and schedulers.
Some scientists at the International Telecommunication Union (ITU) have suggested widening the gap between astronomical and atomic time until a “leap hour” is needed, which would minimize interference with telecommunications. Whether a leap second needs to be added or subtracted is ultimately determined by IERS in Paris, France.
(Comprehensive report by reporter Li Zhaoxi/responsible editor: Lin Qing)
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