The Sun

Properties of the Sun...

  • The radius of the Sun is more than 100x the radius of the Earth.
  • The Sun's mass is about 333,000x the Earth's mass.
  • The Sun is 1AU (93 million miles) from the Earth.
  • Core temp. is 15 million Kelvin, Surface temp is 5780 Kelvin.
  • Composed mainly of hydrogen (71%) and helium (27%).
  • The Sun produces 400,000,000,000,000,000,000,000,000 watts.
Layers of the Sun...

Overview with good pictures here.

  1. The Core
    • 15,000,000 K
    • nuclear fusion occurs here
  2. Radiative Zone
    • Energy moves out from the core by radiation, getting absorbed and re-emitted by atoms every cm or so.
    • It takes the energy 16 million years to get from the core to the convection zone.
  3. Convection Zone
    • energy carried by convection currents in the gas
  4. Photosphere
    • the Sun's visible surface
    • 6,000 K
    • emits the light that we see
    • insulates the inner layers, slowing heat loss
    • granulations - dark zones around bright "bubbles" of hot gas rising up from the convection zone.
  5. Chromosphere
    • the Sun's lower atmosphere 
    • drowned out by the light from the photosphere, but visible during an
    • eclipse or with a special filter
    • 4,500 - 50,000 K
    • spicules - jets of gas coming out of the photosphere.  Photo here.
  6. Corona
    • the Sun's upper atmosphere
    • visible during an eclipse or with a special filter
    • up to 1,000,000 K
    • coronal holes - regions of cooler gas where gas escapes to space

 

The Solar Cycle

  • A cycle of changes in sunspot and solar flare activity.
  • The number of sunspots/solar flares peaks about every 11 years.
    • This influences climate on Earth.
  • This is caused by differential rotation within the Sun.
    • The Sun's equator rotates faster than the Sun's poles.
    • Since the gases of the Sun are bound to the magnetic field, this twists the magnetic field until it creates two magnetic loops inside the Sun.
    • Bulges in the magnetic loops break through the surface of the Sun, creating sunspots, prominences, and flares.
    • The more tightly wound the magnetic fields are, the more bulges form, and the more sunspots appear.
    • Eventually, the magnetic field snaps back into its original place, reversing polarity, and sunspots disappear.
  • Since the Sun's magnetic polarity is reversed by this process, it takes two cycles to return to its original position.  So, a solar cycle is 22 yrs.

 

Web Resources:

 

Homework from the Text:

  • Read Chapter 11 (pg. 323-345).
  • Review Questions #1,4, 5, 6, 8, 10,13,14,17,19,21 (pg. 345-346).
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