In 2025, the 24-hour day of 10 July was shortened by 1.36 milliseconds and two shorter days of similar time scale were predicted on 22 July and 5 August. A millisecond is one-thousandth of a second. Earlier, shortened days were reported since 1960s when the recordings began. After the Sumatra earthquake of magnitude 9.2 in 2004 shortening of a day by 2.68 microseconds was also reported. A microsecond is one thousand times smaller than a millisecond. The exact reasons of speeding Earth’s spin are not known but there are hypotheses like mass distribution of the inner and outer layers of the Earth, ocean levels, tides, earthquakes and the climate. The Earth is an oblate spheroid and due to global warming polar ice melts tending the shape more towards spherical thereby increasing the speed. But this type of speeding is occasional as data shows that Earth’s spin is actually slowing down since its formation when it probably had a 6-hour day, 4.5 billion years ago.
An explanation is offered here that is both speculative and data based. First the speculative part. Our solar system was formed from a moving cloud of gas and dustcalled the planetary nebula. As matter was created around the sun, collisions and gravitational interactions cancelled out all random motions until only a single, net rotation around a plane remained. Later, when matter coalesced into different planets, this net rotation was conservedcausing the planets to spin faster on its own axis as they grew denser. To explain the expression “rotation was conserved” in simpler terms, it means that the total momentum before a collision or interaction is equal to the total momentum after the collision or interaction. This is the law of conservation of momentumthat says that momentum is neither created nor destroyed in a closed system, it can only be transferred between objects within the system, but the total momentum remains the same.
The nascent Earth that was spinning on its axis was then struck by a Mars-sized protoplanet that knocked it askew by 23 degrees to the rest of the solar system giving Earth it’s Moon that is orbiting around it, today. The Moon’s gravity constantly creates a bulge in the Earth mostly as tides in the oceans that are carried eastwards due to daily rotation. In the initial stage, both Earth and Moon were spinning much quicker on their own axes till Moon’s rotational and orbital period were in sync and then its bulge faced the Earth as it became locked. That is why we see only one side of the Moon every day. While the rotation of Earth’s bulge constantly pulls the Moon forward in its orbit, Moon pulls it back toward itself. In this tug-of-war the rotation of the Earth slows down but accelerate Moon’s orbit. The laser range finding experiment that was launched during the Apollo 11 mission in 1969 has shown that the Moon is receding by nearly 4 cm per year slowing down our days on Earth.
