phys0001_chapter06 - Chapter 6 The Solar System and the...

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Chapter 6 The Solar System and the Earth We are going to discuss our solar system. A solar system consists of a star and the objects gravitationally bounded to it, including the planets, comets, etc. We will study stars themselves in the second semester. In this chapter, we will briefly introduce the formation of a solar system, the overview of our solar system and the Earth, our home planet. Formation of a Solar System It is impossible to go back in time to see how our solar system formed, nor can we create a solar system as an experiment. Besides, there is only one solar system that we can examine in details. Then, how do we know? To be honest, we can only guess. But it is an educated guess. The guess should satisfy all known laws of nature and it must be natural, in other words, it cannot be the result of some special initial arrangements. We believe that about 5 billion years ago , there was a large cloud of gas and dust. It contracted by its own gravity. In general, the cloud would also rotate. According to a physical law, if an object rotates and there is no external force, it will keep on rotating. Upon contraction, the rotation of the cloud and the collisions between the particles in cloud would flatten the cloud to a disk, called the accretion disk . The contraction did not stop, it never stops. Materials at the center of the disk contract to form a star, our Sun. Materials not near the center will contract by themselves and form the planets. The rotation of the original gas and dust cloud
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phys0001_chapter06 - Chapter 6 The Solar System and the...

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