Our Star, the Sun. Chapter Eighteen. Guiding Questions. What is the source of the Sun’s energy? What is the internal structure of the Sun? How can astronomers measure the properties of the Sun’s interior? How can we be sure that thermonuclear reactions are happening in the Sun’s core?
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Our Star, the Sun
The Sun’s energy is produced by hydrogen fusion, a sequence of thermonuclear reactions in which four hydrogen nuclei combine to produce a single helium nucleus
Start of hydrogen fusion process in the sun’s interior; 2 protons collide.
Step 2 in the fusion process involves a 3rd proton
In the final step, the end products are helium with 2 of the
original 6 hydrogen atoms recycled.
Energy is transported by radiative diffusion from center to 0.71 solar radii
It takes 170,000 years to traverse through the body of the sun to surface.
Note that only 0.8 % of the sun’s volume is < .2 solar radii
Internal solar densities and temperature, note water is 1000 kg/m3
Temperature in Umbra abt 4400 K, Penumbra abt 5000 K, 30% of light
Tracking the sun’s rotation with sunspots; 25 ¼ days at equator, 28.2 days at latitude 45, 34 days nearer the poles.
Solar Flare Movie
Bright areas or Plages form just before appearance of sunspots
Filaments appear as prominences above solar limb
Bright areas are called Plages,
The magnetic-dynamo model suggests that many features of the solar cycle are due to changes in the Sun’s magnetic field
Coronal Quiet Region
Coronal Active Region
Coronal Mass Ejection
Coronal mass ejections send bursts of energetic charged particles out through the solar system.
Coronal mass ejection of 1012 kg mass ( a billion tons)
22-year solar cycle
coronal mass ejection
luminosity (of the Sun)
negative hydrogen ion