Lecture Notes: The Sun and Our Solar System

Introduction

• Importance of the Sun: Central to our solar system, providing light and heat essential for life on Earth.
• Formation:
  • Formed 4.5 billion years ago in the Milky Way’s Orion Spur.
  • Originated from a solar nebula collapse, leading to a burning ball of gas - our Sun.

Structure of the Sun

• Layers of the Sun:
  • Core: Site of thermonuclear fusion, extremely hot (27 million degrees Fahrenheit).
  • Radiative and Convective Zones.
  • Photosphere: Visible surface of the Sun.
  • Chromosphere.
  • Corona: Outermost layer.

Composition

• Hydrogen: 91% - primary fuel.
• Helium: 8.9%.
• Heavier Elements: Carbon, nitrogen, etc.
• Phase: Plasma due to extreme temperatures.

Energy Production

• Thermonuclear Fusion:
  • Hydrogen converts to helium in the core.
  • Releases energy as radiation, electricity, solar wind, and heat/light.

The Sun’s Gravitational Influence

• Mass and Size:
  • Largest object in the solar system; over 100 Earths wide.
  • Holds 99.8% of the solar system’s mass.
• Gravitational Pull:
  • Holds planets, moons, comets, and asteroids in orbit.

The Magnetic Field and the Heliosphere

• Magnetic Field:
  • Created by plasma movements, making the Sun a giant magnet.
  • Sunspots: Indicate strong magnetic activity.
  • Heliosphere: Protects planets from cosmic radiation.
• Effects:
  • Causes auroras on Earth and other planets.

The Sun’s Lifecycle

• Future:
  • In 6.5 billion years, will exhaust hydrogen fuel.
  • Will expand, engulfing inner planets, and shrink into a white dwarf.

Conclusion

• Continued Role:
  • Provides energy, gravitational stability, and protection via its magnetic field.
  • Essential for the life and structure of the solar system.