Earth’s shortest day
Why in News:
- Earth on July 29 completed a full spin in 1.59 milliseconds less than its standard 24 hours. It was the shortest day recorded since the 1960s, when scientists first began to use the precise atomic clocks to measure the Earth’s rotational speed.
What is Earth’s rotation?
- Rotation is the movement of the earth on its axis.
- Earth rotates along its axis from west to east.
- The axis of the earth, which is an imaginary line, makes an angle of 66½° with its orbital plane. The plane formed by the orbit is known as the orbital plane.
- The circle that divides the day from night on the globe is called the circle of illumination. This circle does not coincide with the axis.
- The earth takes about 24 hours to complete one rotation around its axis. The period of rotation is known as the earthday.
About Earth’s spin
- Earth spins on its axis at about 1,000 miles per hour, or 1,525 feet per second at the equator. This speed maintains our familiar day-night pattern as a 24-hour cycle.
- The Earth’s spin is generally slowing, so a leap second (an extra second every 1.5 years or so) is added to allow it to catch up to the clocks.
- For hundreds of millions of years, the moon’s gravity has been exerting a pull on our planet, causing high tides and slowing down our spin. In fact, the difference between proto-Earth’s days and our modern days is stark; when the Earth-moon system formed about 4.5 billion years ago, Earth spun much faster, making a day last only four hours.
What is the correlation between spin and length of day?
- When the length of day is a positive number and rising, the Earth is spinning slower and vice versa.
Possible Causes for the increase in Earth’s rotational speed
- Researchers still don’t know the reason for the increased speed of Earth’s rotation but they speculate that processes in the inner or outer layers of the core, oceans, tides, transfer of angular momentum from its interior to the outside, the oxygenation of its atmosphere. or even changes in climate could be the reason.
- Anything that changes the composition and distribution of material on the Earth’s surface can also have this effect.
- Some also believe that the movement of Earth’s geographic poles across its surface, or the “Chandler wobble” could also be the reason.
- The Chandler Wobble refers to a small deviation in the Earth’s axis of rotation relative to solid earth. The Earth also wobbles because of the fact that its axis of rotation is tilted with respect to the geographical axis and a change in this angle can cause a variation in rotation time too.
- The Earth’s magnetic field is produced by convection that occurs in the outer core, creating waves. These are called torsional waves. They originate from the outer core or from the fluctuations of buoyancy in the inner molten core. We can think of these as concentric cylinders that oscillate back and forth, all the way from the inner core to the mantle, creating waves that travel outward and this has been correlated to the length of day for a century now.
- Another plausible reason could be the melting of glaciers and polar ice caps that result in a change of mass distribution on the surface or interior of the Earth. If ice melts rapidly or continuously in a particular region of the planet, it could cause a tip in balance.
- To some extent, tidal waves and tidal motion can also contribute to the variations in the length of night and day and can indirectly be associated with climate change.
Is there a cause to worry?
- Earth does periodically slow down and speed up in its rotation about its axis. This is a wavelike change.
- If Earth continues to rotate at an increasing rate, negative leap seconds would need to be introduced to keep the rate of the planet orbiting the Sun consistent with the measurement from atomic clocks
- However, the introduction of negative leap second can confuse smartphones, computers and communications systems and can do more harm than good
- Tech giants like Meta have apparently raised an issue as it could necessitate the adding of a leap second, which may in turn affect software that has been programmed to display time a certain way.
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