Solar Interior Lecture Notes

Introduction

• Discussion on the properties of the Sun and its opacity.
• Focus on the solar interior, primarily theoretical.
• Theories must align with observations to be credible.

Solar Interior Model

• Based on mathematical models and physics laws.
• Balance in the Sun
  • Gravitational pressure (inward) vs. outward pressure.
  • Equilibrium when both forces are equal, maintaining the Sun's size.

Observations through Doppler Shifts

• Earth satellites and spacecraft observe the Sun continuously.
• Doppler Shifts
  • Redshift: Parts moving away from Earth.
  • Blueshift: Parts moving toward Earth.
• Indicates the Sun is vibrating.

Helioseismology

• Study of the Sun's interior through surface vibrations.
• Helioseismology allows deduction of the Sun’s interior structure.
• Comparison with seismology on Earth.
• No physical seismographs on the Sun, purely theoretical.

Sun's Vibrations

• Sun vibrates like a resonant bell.
• Sun is not a solid but has solid-like properties in parts.
• Density increases toward the solar core.

Solar Layers

• Core: Site of nuclear fusion, extremely dense.
• Radiation Zone: Energy transported by photons.
• Convection Zone: Outer layer, energy transported by convection similar to a boiling process.
• Photosphere: Visible surface of the Sun.

Density and Temperature

• Density
  • Highest at the core (100,000 times water density).
  • Drops off rapidly towards the surface.
• Temperature
  • Core temperature nearly 16 million Kelvins.
  • Drops to 5800 Kelvins at the surface.

Conclusion

• Understanding the solar interior involves both theoretical models and observational evidence.
• Next focus: Energy transport in the convection zone, the outermost layer of the solar interior.