From UPSC perspective, the following things are important :
Prelims level : Earth's spin
Mains level : Read the attached story
On June 29, the Earth completed one full spin — a day — in 1.59 milliseconds less than its routine 24 hours. It was the shortest day recorded since the 1960s.
Note: A millisecond is one-thousandth of a second.
Earth spinning faster
- While the Earth has been completing its rotations faster in recent years, when looked at over a much longer period of time, our planet is actually spinning slower.
- Every century, the Earth takes a few milliseconds longer to complete one rotation — and on average, days are actually getting longer.
- So, 1.4 billion years ago, a day would have ended in less than 19 hours,
How did scientists find that?
- Scientists got to know by using precise atomic clocks to measure the Earth’s rotational speed.
Why are days getting shorter these days?
- Scientists aren’t entirely sure.
- Something has changed and changed in a way we haven’t seen since the beginning of precise radio astronomy in the 1970s.
Factors attributing Earth’s Spin
(1) Tidal Braking
- The research attributed the larger trend of the Earth’s slower spin mostly to the gravitational pull of the Moon, which causes tidal friction and slows down the Earth’s rotations.
(2) Climate change-induced surface variations
- Melting ice sheets in Greenland and Antarctica
- Changes in ocean circulation
(3) Geomorphic factors
- Movements in the planet’s inner molten core
- Seismic activity
- Wind speed, and shifting atmospheric gases
(4) Chandler wobble phenomenon
- This refers to the small deviation in the movement of Earth’s geographical poles.
- The normal amplitude of the Chandler wobble is about three to four metres at Earth’s surface, but from 2017 to 2020 it disappeared.
(5) Other propositions
- Activities that push mass towards the centre of the Earth will hasten the planet’s rotation.
- Anything that pushes mass outwards will slow down the spin, a report noted.
What can happen if the Earth continues to spin faster on a sustained basis?
- To ensure that the time on clocks matches the speed of the Earth’s rotation, a system of leap seconds has been used since the 1970s.
- They involve one-second adjustments to Universal Coordinated Time (UTC), the time standard used to synchronize clocks around the world.
- Due to the long-term slowing in the planet’s spin, 27 leap seconds have been added to UTC.
- However, if the Earth continues to spin faster and days subsequently become shorter, scientists may have to introduce the first ever ‘negative leap second,’ which involves subtraction of a second from clocks.