For the first time that the Earth revolves around its axis, said in his research, in the early 16th-century Italian scientist. But the reason why the rotation occurs always been a lot of controversy in the scientific community. One of the most common theories says that during the rotation of the earth's main role was played by other processes – those that were in ancient times, when only began the formation of planets. "Huddled together" clouds of cosmic dust, and thus formed the "germ" of the planets. Then "attract" other space bodies – large and smaller. It is the collision with a large celestial bodies, according to some scientists, due to the constant rotation of the planets. And then, according to the theory, the planets continued by inertia rotation. However, if you take into account this theory raises many valid questions. Why in the Solar system of six planets rotate in one direction and another in opposite Venus? Why is the planet Uranus rotates in such a way that on this planet does not change the time of day? Why is the speed of earth's rotation can vary (slightly, of course, but still)? To all these questions scientists have yet to answer. It is known that the Ground tends to slow down its rotation. Each century increases the time of a full revolution about the axis around 0,0024 seconds. Scientists attribute this to the influence of Earth's satellite – the moon. Well, about the planets of the Solar system, we can say that the "slow" rotation of the planet Venus is considered the fastest – Uranium.