Overview Of Astronomy


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Overview Of Astronomy

  1. 1. Objectives: <ul><li>Describe the importance/ value/benefit of Astronomy </li></ul><ul><li>Clearly describe our place in the cosmos and the universe at various scales </li></ul>Overview of Astronomy
  2. 2. 1/ What is the value/benefit of Astronomy? <ul><li>Scientific and Technological </li></ul><ul><ul><li>Physics Laws; Satellites and Rockets; Materials, etc. </li></ul></ul><ul><li>Practical </li></ul><ul><ul><li>Geography; Time-keeping; Religious Injunctions; etc. </li></ul></ul><ul><li>Philosophical </li></ul><ul><ul><li>Our place in the Cosmos; Creation; etc. </li></ul></ul>
  3. 3. Astronomical distances and sizes are so large that astronomers use special units Astronomical Unit (AU) – applicable inside the solar system = average distance between Sun and Earth = 150,000,000 km = 1.5 x 10 8 km Light-Year (ly) – applicable between stars and galaxies = distance light travels in one year = ~ 9 x 10 12 km
  4. 4. The Solar System: <ul><li>The Sun: Our nearby star, at 1 AU = 150 million km away, or just 8 minutes of light travel time, and 100 times the diameter of the Earth; the energy we use on Earth initially comes from nuclear reactions in its core. </li></ul><ul><li>Four Small, Rocky Terrestrial Planets </li></ul><ul><li>+ asteroids (belt) </li></ul><ul><li>Four Large, Gaseous Jovian Planets </li></ul><ul><li>+ “Dwarf Planets” : Pluto + Eris + Sedna… </li></ul>Scale of the Universe and Overview of Contents
  5. 5. <ul><li>Outskirts of the Solar System </li></ul><ul><li>Comets: Icy objects, in elliptical orbits. They can enter the inner Solar System and sometimes hit planets. </li></ul>
  6. 6. Stars and Other Things in the Galaxy <ul><li>Stars: From dwarfs to supergiants; the nearest one is Alpha Centauri, a triple star system at 4.34 ly = 40,000 billion km (~ 300,000 AU), visible from the Southern Hemisphere (only). </li></ul><ul><li>Between stars: </li></ul><ul><li>Nebulae (clouds) and interstellar matter. </li></ul>
  7. 7. <ul><li>Do those stars have planets? So far, we've found more than 400, and we've just begun (since 1997). </li></ul>
  8. 8. <ul><li>Our “country”: The Milky Way </li></ul>100,000 light years across, contains ~ 200 billion stars. <ul><li>A useful analogy: Universe and Earth Geography </li></ul><ul><li>City and Neighborhood </li></ul><ul><li>Country </li></ul><ul><li>Continents… </li></ul><ul><li>Our “city”: The Solar System </li></ul>Downtown (Sun) and Neighborhoods (Planets).
  9. 9. Other Galaxies and the Rest of the Universe <ul><li>Other Galaxies: Spiral, elliptical, or irregular. </li></ul><ul><li>How many are there? About 100 billion in the visible universe, arranged in clusters and superclusters and moving away from us. </li></ul><ul><li>Our neighbor countries: </li></ul><ul><li>The Local Group (of ~ 20 galaxies), ~ 3 million light-years across. </li></ul><ul><li>The Andromeda Galaxy is our nearest neighbor, about 2 million light-years away. </li></ul>
  10. 10. <ul><li>The Universe is also expanding , everywhere, in all directions, since the Big Bang, and the most recent observations seem to imply that it will probably expand forever… </li></ul><ul><li>(More on this later.) </li></ul><ul><li>The Universe : A size of ~ 10 23 km! </li></ul><ul><li>A “size” of the Universe can be determined from its age and from knowing how fast light travels from one region to another (speed of light = 300000 km/s). The most recent age of Universe (determined in January 2003) is 13.7 billion years... </li></ul>
  11. 11. Graphical Summary of the scale levels of the Universe, from the Earth, to the Solar System, to the Galaxy, to the Universe as a whole! Powers of Ten movie