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Overview Of Astronomy
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Overview Of Astronomy


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  • 1. Objectives:
    • Describe the importance/ value/benefit of Astronomy
    • Clearly describe our place in the cosmos and the universe at various scales
    Overview of Astronomy
  • 2. 1/ What is the value/benefit of Astronomy?
    • Scientific and Technological
      • Physics Laws; Satellites and Rockets; Materials, etc.
    • Practical
      • Geography; Time-keeping; Religious Injunctions; etc.
    • Philosophical
      • Our place in the Cosmos; Creation; etc.
  • 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. The Solar System:
    • 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.
    • Four Small, Rocky Terrestrial Planets
    • + asteroids (belt)
    • Four Large, Gaseous Jovian Planets
    • + “Dwarf Planets” : Pluto + Eris + Sedna…
    Scale of the Universe and Overview of Contents
  • 5.
    • Outskirts of the Solar System
    • Comets: Icy objects, in elliptical orbits. They can enter the inner Solar System and sometimes hit planets.
  • 6. Stars and Other Things in the Galaxy
    • 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).
    • Between stars:
    • Nebulae (clouds) and interstellar matter.
  • 7.
    • Do those stars have planets? So far, we've found more than 400, and we've just begun (since 1997).
  • 8.
    • Our “country”: The Milky Way
    100,000 light years across, contains ~ 200 billion stars.
    • A useful analogy: Universe and Earth Geography
    • City and Neighborhood
    • Country
    • Continents…
    • Our “city”: The Solar System
    Downtown (Sun) and Neighborhoods (Planets).
  • 9. Other Galaxies and the Rest of the Universe
    • Other Galaxies: Spiral, elliptical, or irregular.
    • How many are there? About 100 billion in the visible universe, arranged in clusters and superclusters and moving away from us.
    • Our neighbor countries:
    • The Local Group (of ~ 20 galaxies), ~ 3 million light-years across.
    • The Andromeda Galaxy is our nearest neighbor, about 2 million light-years away.
  • 10.
    • 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…
    • (More on this later.)
    • The Universe : A size of ~ 10 23 km!
    • 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...
  • 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