The Sun: Structure and Behavior

Basic Facts About the Sun

• Located at the center of the solar system.

• Average-sized star.

• Diameter: $1,393,000$ kilometers (109 Earths could fit across).

• Mass: 1.989 oldsymbold × 10^{30} kilograms (equal to 333,000 Earths).

• Distance from Earth: $149,600,000$ kilometers.

• Age: Approximately 4.6 billion years old.

• Composition: 71% hydrogen, 27% helium, 2% other elements.

• Surface temperature: About $5,500$ degrees Celsius.

Interior of the Sun

• Core:

  • Innermost layer.

  • Energy produced through nuclear fusion.

  • Temperature: $15,000,000$ degrees Celsius.

• Radiation Zone:

  • Surrounds the core.

  • Energy moves via radiation.

  • Temperature varies: $7,000,000$ to $2,000,000$ degrees Celsius.

• Convection Zone:

  • Outermost layer.

  • Energy transferred through convection currents.

  • Temperature: About $2,000,000$ degrees Celsius.

Atmosphere of the Sun

• Photosphere:

  • Lowest layer, visible white light.

  • Thickness: About 100 kilometers.

  • Temperature: About $5,500$ degrees Celsius.

• Chromosphere:

  • Middle layer.

  • Thickness: About 2,000 kilometers.

  • Temperature: $6,000$ to $20,000$ degrees Celsius.

• Corona:

  • Outermost layer, visible during solar eclipses.

  • Extends millions of kilometers into space.

  • Temperature: Around $2,000,000$ degrees Celsius.

Energy Production: Nuclear Fusion

• Process: Lighter nuclei combine to form a heavier nucleus.

• Ingredients: Hydrogen gas, extreme heat, and pressure.

• Process: Hydrogen atoms combine to form helium, releasing energy.

• $4$ hydrogen atoms → 1 helium atom + energy (mass converted to energy).

Solar Activity

• Sunspots:

  • Dark, cooler areas on the surface.

  • Occur in groups, vary in size.

  • Sunspot cycle: 11-year period.

• Solar Flares:

  • Sudden energy eruptions.

  • Extend into the corona.

  • Temperature: $10,000,000$ to $20,000,000$ degrees Celsius.

  • Can disrupt radio communications.

• Prominences:

  • Eruptions of material forming loops.

  • Gas cooler and denser than surroundings.

  • Disrupt radio communications.

• Solar Wind:

  • Stream of charged particles from the corona.

  • Speed: 400 kilometers per second.

  • Interacts with Earth's magnetic field, causing aurora.

  • May disrupt satellite communication.

Astronomical Units (AU)

• An astronomical unit (AU) is the average distance between the Earth and the Sun.

• 1 AU = $149,597,870.7$ kilometers.

Earth's Magnetic Field

• Earth's magnetic field results from the constant motion of metals in Earth's outer core and Earth's rotation.

• Van Allen Belts: Radiation zones that trap high-energy particles, protecting Earth.

Sun's Lifespan

• Based on mass about 10 billion years.

• Current stage: Main sequence (converting hydrogen to helium).

• Nebula: Cloud of dust, hydrogen, and helium.

• Protostar: Spherical shape formed due to gravity and collision of atoms.

• Red Giant: Expansion due to helium fusion, potentially engulfing inner planets.

• White Dwarf: Final stage after fusion slows, matter pulled into the core.