If you have seen any of the films taken by the astronauts in outer space, you know that the earth spins. It spins so slowly that living here, we don’t even notice it. The spin is in a counter-clock-wise direction (backwards from the direction of a clock) and the funny part is: almost all of the planets in our solar system spin in the same direction.
To understand why the earth spins, we have to go back in time to see how our solar system was created. In the deep reaches of space, gas and dust clouds form in what is called a ‘nebula’. These are the birthplace of stars. As they swirl and spin the dust collects together and pressure builds up. Like shaking up a soda can, when the pressure is released, it sprays out. In the case of a nebula, it can create stars. It’s also thought that it takes a special event, like the explosion of another star going ‘nova’ to finally blast everything out. The explosion causes the star and all of the dust and dirt to spin. Since everything was hit in the same direction from the explosion, they spin in the same direction.
There’s so much dust that has gathered together that pieces begin to slam into each other, eventually forming asteroids and these are pulled in by the gravity of the spinning star. This goes on for billions of years, with everything bumping and crashing together. Bigger and bigger pieces are formed as the asteroids collide and stick together, all the while they are all spinning in the same direction.
Remember that star that was created? Well, it has gravity that slowly pulls all of the asteroids, dust, dirt and everything else in towards it. This process creates even more collisions until finally they form what will be planets. In almost all cases, even crashing into each other doesn’t change the direction that they are spinning. That’s how powerful the explosion was. The star that is in the center of all of this chaos, is becoming a future sun. But it doesn’t settle down quite yet.
During this time, the future ‘planets’ are circling around this new sun, but things are still quite unstable. As they cool and spin, they can also collide into each other, forming bigger planets, with the left over pieces forming what will be moons. The gravity of the sun continues to pull for billions more years until the planets settle into their rotation around the sun, leaving plenty of room for each other so they don’t collide.
If we had been out in a spaceship, watching all of this happen, we would notice that all of the planets are still spinning in that same original direction. Some spin faster than others, but all are spinning and slowly circling around the sun in their own path. We would also see the various moons around the planets. These can spin in the same direction as the planet or completely opposite, because they were created after the original explosion.
So we can say that the earth is spinning because it was part of an explosion that caused the birth of our sun and solar system and that explosion was so incredible that it has kept the planets spinning. Since there is nothing to stop it, the earth will continue to spin.
archive.org - Another video of the Earth