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chapt 1isp notes - Chapter One Cosmic Address You Earth...

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Chapter One Cosmic Address: You, Earth, Solar System, Milky Way Galaxy, Local Group, Local Supercluster, universe In what sense are we “star stuff” : nearly every atom from which we are made was once inside of a star, all but the hydrogen was produced by fusion inside of stars. How are galaxies important to our existence? Galaxies recycle material from one generation of stars to the next, without this recycling we could not exist. Many of the elements in our bodies were made inside stars by nuclear fusion, without galactic recycling, our solar system could not have contained these elements. When we look at an object that is 1,000 light years away we see it… as it was 1,000 years ago. It takes light 1,000 years to travel 1,000 light years, so we see the object as it was 1,000 years ago. Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In that case: we are seeing Galaxy 1 as it looked at an earlier time in history of the universe than Galaxy 2.-- Galaxy 1 is farther, so we are seeing it at a time further into the past. Suppose we make a scale model of our solar system, with the Sun the size of a grapefruit. Which of the following best describes what the planets would look like? They are all much smaller than the Sun. Four planets are within about 20 meters of the Sun, while the next four planets are spread much farther apart. How long would it take to count all the stars in the Milky Way Galaxy at a rate of one star per second? Several thousand years. Total number of stars in the observable universe is about: the same as the number of grains of sand on all the beaches on the Earth
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