The Sun

Outline

• Introduction
• The Sun's Structure
  • Energy Transfer
  • Energy Production
  • Solar Characteristics

The Sun's Structure

Review the homework study guide notes, which are fairly extensive.

Putting it all together: the sun's structure and layers.

• The lower left half of the diagram shows the source of light of different energy levels.
  • Visible light (top wedge): The photosphere surface is the source of the visible light we see. Small convection zones on the surface are responsible for granularity which creates bumps. Cool areas appear as sunspots, with a central dark area or umbra surrounded by a lighter area, the penumbra. Don't let these terms confuse you: we are not talking about shadows here.
  • Hydrogen alpha (middle wedge): Most light at this frequency comes from the chromosphere, but some comes also from surface eruptions in the photosphere, from spicules, filaments, and plages.
  • Ultraviolet and X-ray (bottom wedge): Most high-energy radiation comes from the corona, but hot sunspot eruptions can also produce X-ray phenomena capable of disrupting communication systems on earth.
• The upper right half of the diagram shows the layers of the sun.
  • The core has a radius 1/4 of the total solar radius. Temperatures are in the million Kelvin, and density (160 gm/cm³) is about 30 times that of the Earth's average density (5 gm/cm³). Nuclear fusion of hydrogen to helium occurs in the core, and energy flows out by photon radiation.
  • The middle level of the sun is the radiation layer, where density prevents circulation of gases and energy transfers by photon radiation.
  • The convection layer allows hotter areas to circulate upward, cool, and fall backward. Eruptions through the photosphere create sunspots.
  • The photosphere is the source of light we can see, and has a temperature of about 5600K.
  • The chromosphere is a rarified atmospheric layer which absorbs heat from below and re-radiates it at higher temperatures. Eruptions from the photosphere release gas particles into this atmosphere, replace particles which have escaped through the coronal streamers and solar wind.
  • The highest level of the sun is the corona, which extends outward millions of miles and is constantly changing shape as the solar magnetic field changes.

Another way to look at the layering in the sun is to focus on energy transference between layers. This diagram shows how energy is transfered by radiation, convection, and conduction at different levels, and how the temperature and pressure vary at each level.

Sunspots and Current Activity

As of February, 2023

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