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PHY134 Introductory Astronomy

PHY134 Introductory Astronomy . The Solar System. 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 )

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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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