The Sun Structure and Atmosphere

The Sun is the heart of our solar system — providing light, heat, and gravitational stability.

Key Facts:

• Age: ~4.6 billion years
• Diameter: ~1.39 million km
• Surface temperature: ~6,000°C
• Core temperature: ~16 million°C
• Mass: ~3,32,900 times that of Earth
• Rotation speed: ~7179 km/h (Earth’s is ~1675 km/h)
• Rotation period: ~25.4 days (varies slightly at different latitudes)
• Composition: ~98% hydrogen and helium
• Gravity: ~274 m/s² (Earth’s gravity is 9.8 m/s²)

While the Sun holds ~99.8% of the solar system’s mass, it has only ~2% of the system’s angular momentum, largely due to its gaseous and differential rotation.

Internal Structure of the Sun

Let’s travel from core to corona:

Solar Interior

1. Core: Site of nuclear fusion — hydrogen atoms fuse to form helium, releasing energy.
2. Radiative Zone: Energy moves outward slowly through radiation.
3. Convective Zone: Energy is transferred through convection currents.

Solar Atmosphere

1. Photosphere:
   • The visible surface of the Sun.
   • Uneven and grainy texture.
   • Temperature: ~6,000°C.
2. Chromosphere:
   • A thin layer of burning gases above the photosphere.
   • Cooler than photosphere (~4,320°C).
3. Corona:
   • Outermost plasma layer, visible during total solar eclipses.
   • Temperature: millions of degrees, source of solar wind.

☀️ Phenomena Associated with the Sun

Sunspots

• Dark patches on the photosphere.
• Caused by magnetic disturbances that block convection.
• Cooler than surroundings (by ~500–1500°C).
• Each spot has:
  • Umbra (dark center)
  • Penumbra (lighter outer zone)
• Sunspots appear in 11-year cycles:
  • Solar Maximum: High activity
  • Solar Minimum: Low activity
• Impact: Even a 1% change in solar energy due to sunspots can influence Earth’s climate

Solar Wind

• Stream of charged particles (plasma) flowing from the Sun.
• Speed: Up to 900 km/s
• Temperature: ~1 million °C
• Interacts with Earth’s magnetic field to cause auroras.

Aurora

• Light displays near poles caused by solar wind particles hitting Earth’s atmosphere.
• Northern lights: Aurora Borealis
• Southern lights: Aurora Australis

⚡ Plasma — The Fourth State of Matter

Beyond solid, liquid, and gas — plasma is:

• An ionised gas with free electrons and ions.
• Found in stars, lightning, neon lights, and even in space.
• Plasma behaves very differently from ordinary gases — it’s highly conductive and influenced by magnetic fields.

Solar Flares

• Sudden, bright magnetic storms on the Sun.
• Can heat gases up to 20 million°C.
• Affects communication systems and satellites on Earth.

Solar Prominence

• Huge arcs of glowing gas suspended by magnetic fields.
• Can extend hundreds of thousands of miles into space.
• Often lasts months.