Lecture 18. The Sun

A. Class Business --

  1. Planet Viewing: what time?
  2. Midterm grades -- by Wed., I hope!

B. The Sun

  1. RADIATION -- again -- Look in different wavelengths, see different stuff!*

    • different temperature gasses emit THERMAL RADIATIONin different wavelengths -- two examples:
      1. hot corona (2 MK) emits in X-rays
      2. photosphere (5800 K) emits in yellow, visible

    • photons in these various wavelength bands are ABSORBED and EMITTED by e-'s (electrons) orbiting atoms
      -- so we also see SPECTRAL LINES


  2. the Sun is so hot, it has IONIZED much of its gas --
    free e-'s and p+'s (protons) and IONS (atoms missing one or more e-) -- a PLASMA

    • hotter particles move faster, colliding all the time
    • at high enough T, collisions between them cause e-'s to be knocked off of atoms
    • if you have a plasma, you'll have MAGNETIC FIELDS




  3. Magnetic Fields

    • "If it weren't for its magnetic field, the Sun would be a pretty boring star." -- quite so!
    • field lines -- show direction & strength of field
      • i) also called "lines of magnetic FLUX"
        -- impress your friends
      • (all magnets have (+) & (-) poles -- BIPOLE
        -- sunspots are bipolar)
      • ii) lines run from (+) to (-) -- FOOTPOINTS of LOOPS (can run in circles, too)
      • iii) more field lines in a given space =
        more flux = stronger field
      • iv) charged particles must follow field lines:
        1. If you move lines, then particles move, too.
        2. If you move particles, then lines move, too.
        3. We say "flux is FROZEN IN to plasma."


  4. VIDEO