Throughout the first five chapters of this book, we have primarily been laying a foundation for our exploration of the cosmos. The first unit in the cosmos ior us to study is logically the solar system, ior it is the sun and its attendant planets among which our home, the earth, is located. Yet for purposes of study there is an awkward mixture of bodies in the solar system:
For example, the sun is a star-a very different kind of body from planets, or satellites, or asteroids, or comets; therefore we shall delay a detailed discussion of the sun and instead use it to introduce our discussion of stars.
Words define common human experience, which does not include direct contact with such entities as other planets or stars. So scientists use numbers to compare objects, and in this chapter we try to give you some sense of the scale of the solar system and the things in it.
