Overview Of Astronomy1
- 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