Structure of the Universe Essays

6149 Words Nov 21st, 2012 25 Pages
Chapter 1: Our Place in the Universe 1.1 Our Modern View of the Universe * Geocentric universe: Earth-centered * Solar system: the Sun and all the objects that orbits it * Our solar system formed 4.5 billion years ago * Galaxy: great island of stars in space, having from a few hundred million to a trillion or more stars * Milky Way Galaxy contains more than 100 billion stars; our Milky Way is in the Local Group * Galaxy cluster: collection of galaxies bound together by gravity. Small collections (up to a few dozen) are generally called groups, while larger collections are called clusters * Supercluster: gigantic region of space where many individual galaxies and many groups and clusters of galaxies are …show more content…
Other elements were manufactured by stars, some through nuclear fusion that makes stars shine and others through nuclear reactions accompanying the explosions that end stellar lives * Speed of light is 3.0 x 10^8 m/s * Light takes about 1 second to reach Earth from the Moon, and 8 minutes from Sun to Earth * Light-year: the distance that light can travel in 1 year, about 10 trillion kilometers * Astronomical unit (AU): the average distance between Earth and the Sun, which is about 150 million kilometers. 1 AU is the length of the semimajor axis of Earth’s orbit * Rotation: the spinning of an object around its axis * Orbit (revolution): the orbital motion of one object around another * Expansion (of universe): the increase in the average distance between galaxies as time progresses 1.2 The Scale of the Universe * Nearest star system to our own is a three-star system called Alpha Centauri, which is 4.4 ly away 1.3 Spaceship

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