Chapter 1 Summary - M01_BENN0885_05_SE_C01.qxd 9/19/08...

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Chapter 1 Our Place in the Universe 21 other galaxies move away from us at speeds that increase with distance in our expanding universe. Spaceship Earth is carrying us on a remark- able journey. the big picture Putting Chapter 1 into Context In this Frst chapter, we developed a broad overview of our place in the universe. As we consider the universe in more depth in the rest of the book, remember the following “big picture” ideas: Earth is not the center of the universe but instead is a planet orbiting a rather ordinary star in the Milky Way Galaxy. The Milky Way Gal- axy, in turn, is one of billions of galaxies in our observable universe. We are “star stuff.” The atoms from which we are made began as hydrogen and helium in the Big Bang and were later fused into heavier elements by massive stars. Stellar deaths released these atoms into space, where our galaxy recycled them into new stars and planets. Our solar system formed from such recycled matter some years ago. Cosmic distances are literally astronomical, but we can put them in perspective with the aid of scale models and other scaling tech- niques. When you think about these enormous scales, don’t forget that every star is a sun and every planet is a unique world. We are latecomers on the scale of cosmic time. The universe was al- ready more than half its current age when our solar system formed, and it took billions of years more before humans arrived on the scene. All of us are being carried through the cosmos on spaceship Earth. Although we cannot feel this motion, the associated speeds are sur- prisingly high. Learning about the motions of spaceship Earth gives us a new perspective on the cosmos and helps us understand its nature and history. 4
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Chapter 1 Summary - M01_BENN0885_05_SE_C01.qxd 9/19/08...

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