The Earth rotates once a day on its axis, making sunrises and sunsets a regular occurrence on the globe. It has done so since its formation 4.6 billion years ago, and it will do so until the world dies – most likely when the sun expands into a red giant star and absorbs the planet. But why does it spin in the first place?
A disk of gas and dust whirled around the newborn sun, forming the Earth. According to Space.com, a sister site of Live Science, pieces of dust and rock stuck together to create the Earth in this rotating disk as the planet increased in size, space objects collided with it, causing it to spin, according to Smadar Naoz, an astronomer at the University of California, Los Angeles. Because all of the debris in the early solar system rotated in the same direction around the sun, the impacts spun the Earth — and much of the rest of the solar system — in the same way.
But, in the first place, why was the solar system spinning? When a cloud of dust and gas fell under its weight, the sun and the solar system were born. The majority of the gas condensed to become the sun, while the rest went into the planet-forming disk around it. The gas molecules and dust particles were moving all over the place before it collapsed, but at some point, some gas and dust shifted a little more in one direction, causing it to spin. The cloud’s rotation accelerated when the gas cloud contracted, similar to how figure skaters spin faster when their arms and legs are tucked in.
Because there isn’t much in space to slow things down, once anything begins to rotate, it typically continues to rotate. In this situation, the revolving newborn solar system possessed a lot of angular momentum, which is a number that defines an object’s inclination to keep spinning. Consequently, when the solar system began, all of the planets most likely rotated in the same direction.
On the other hand, some planets have put their twist on their motion today. Uranus’ spin axis is tilted 90 degrees, while Venus rotates in the opposite direction as Earth. Scientists are unsure how these planets came to be in this state, but they have some theories. Venus’ rotation may have flipped due to a collision. Or it might have started spinning like the other planets. The spin of Venus flipped overtime when the sun’s gravitational pull on the planet’s heavy clouds interacted with friction between the planet’s core and mantle. Venus’ rotation may have slowed and reversed due to gravitational interactions with the sun and other variables, according to 2001 research published in Nature.
According to Scientific American, experts believe Uranus was thrown off kilter by impacts – one large collision with a large rock or even a one-two punch with two different things.
Regardless of such perturbations, everything in space spins in one of two directions. “In the cosmos, rotating is a basic characteristic of things,” Naoz said.
Asteroids move about in space. The stars move about. According to NASA, galaxies move around in space (it takes 230 million years for the solar system to complete one circuit around the Milky Way). Pulsars, dense, spinning objects that are the remains of huge stars, are some of the fastest things in the universe. Pulsars may spin hundreds of times per second and have a diameter of approximately the size of a metropolis. The fastest, Terzan 5ad, was disclosed in Science in 2006 and spins 716 times per second.
Even quicker are black holes. According to a 2006 research published in the Astrophysical Journal, one of them, GRS 1915+105, might be spinning anywhere between 920 and 1,150 times per second.
Things do, however, slow down. According to Naoz, the sun rotated once every four days when it was created. Today, though, it takes around 25 days for the sun to rotate once, according to her. According to Naoz, its magnetic field interacts with the solar wind to delay its spin.
Even the Earth’s rotation slows down. The moon’s gravity pulls on Earth in such a manner that it somewhat slows it down. An examination of ancient eclipses published in the journal Proceedings of the Royal Society A in 2016 found that Earth’s rotation slowed by 1.78 milliseconds over a century.