Why Does the Earth Rotate?
Written by Fraser Cain
The rotation of our planet has an impact on almost all life on Earth. As the Earth turns on its axis, each part of the planet gets a chance to face the Sun and be warmed in a relatively short period of time.
You could get a situation where there's no rotation. In this case, a day would take an entire year, and it would only happen because of the Earth's orbit around the Sun – Earth wouldn't actually be turning in space. You could get another situation, where the Earth was tidally locked to the Sun, and the rotation was the same length of time as the year. In this case, Earth would always show the same face to the Sun – half the planet would be frozen, and the other half would be hot.
Fortunately, the Earth does rotate, giving us days every 24 hours. But why does the Earth rotate?
Earth rotates because of leftover momentum from the solar nebula that all of the planets and the Sun formed within. The solar nebula collapsed when a supernova sent a shock through a cold cloud of molecular hydrogen. Each molecule in the cloud had its own momentum, and as they came together, their momentums added up, and needed to be conserved. This set the solar nebula spinning, and created the planetary disk.
As the planetary disk flattened out, each of the planets clustered together from gravity. Over time they accumulated more and more material. And once again, the rotation of the planet was caused by the addition of all the momentum of the particles that came together. This is why all of the planets (except Venus) rotate in the same direction.
It's believed that major collisions early on in the Solar System might have changed the planets' rotation. One collision might have sent Venus spinning in retrograde, and another might have caused the current 23-degree tilt in the Earth's axis.
Because space is a vacuum, there is nothing that will stop the rotation of the Earth or any of the planets. Like spinning tops that don't experience any friction, they'll just keep on spinning forever.
Filed under: Astronomy
