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PHY134 Introductory Astronomy

This introduction to astronomy explores how light interacts with matter in the solar system, examining phenomena like absorption, reflection, and scattering. It discusses how the sun's spectrum reveals gaps and the significance of line spectra for determining chemical composition. The presentation of the solar system covers planet classifications, such as rocky inner planets and gas giants, examining their orbits and composition. Key questions about the nature of planetary formation, the characteristics of moons, rings, and the history of asteroids provide deeper insights into our cosmic neighborhood.

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PHY134 Introductory Astronomy

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  1. PHY134Introductory Astronomy The Solar System

  2. When Light Meets Matter • Dense objects absorb light energy or reflect it. • How much absorbed can depend on wavelength – dyes. Can learn composition from reflected spectrum • Light scatters off tenuous matter (Rayleigh 1871) • Scattering decreases with wavelength: blue scatters more than red

  3. Scattering on Earth • Atmosphere scatters blue light making sky glow blue and Sun appear yellow • When we get more scattering – when Sun low in sky – lose green to scattering leaving Sun red

  4. Scattering and Refraction Moon halo Rainbow

  5. Line Spectra • Fraunhofer 1814: Sun’s spectrum has gaps • Kirchoff-Bunsen 1859: Tenuous gas emits line spectrum • Atoms and molecules emit/absorb at characteristic wavelengths when heated or ionized • Line spectrum yields chemical composition • At higher pressure and density lines broadened

  6. Solar System - Inventory • Mostly, Solar system is an average ( ) main sequence star • Sun contains about of the bound mass • Radiation heats planets • Solar wind – charged particles streaming from Sun at high energy carry in

  7. What is Out There • Eight planets orbit Sun in slightly eccentric elliptic orbits • Radius • Orbits near ecliptic match Sun rotation

  8. Two Kinds of Planets • Four Inner planets within 1.6 AU • Dense • Small • Rocky • Four Outer planets from 5-30 AU • Less dense • Huge • Fluid

  9. What Else? Lots of Moons Rings

  10. Craters

  11. Asteroids

  12. Farther Out

  13. What it’s Made Of • of mass is Sun • of rest is Jupiter, Saturn • Hydrogen • Helium • Metals

  14. Questions • Why are all planet orbits circular and in a plane? Why aren’t comets’? • Why are planets and large Moons round? • Why aren’t asteroids? • Why are inner planets small, rocky, dense while outer planets are large, fluid, light? • Why aren’t asteroids a planet? • What is the story with Pluto? • What are rings? Why are Saturn’s different? • What made all the craters? Where did it go? • Why do comets fall into inner Solar System? Why do asteroids fall into near-Earth orbits? • If orbits can change – will planet orbits? Have they? • Where did it all come from? When?

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