THE SUN

• Age: ~4.6 billion years
• Diameter: ~1.39 million km
• Surface Temperature: ~6000 °C
• Core Temperature: ~16 million °C
• Mass: ~3,32,900 times Earth
• Composition: ~98% Hydrogen & Helium
• Gravity: 274 m/s² (≈28× Earth)
• Rotation Period: ~25 days 9 hours (differential rotation)
• Rotation Direction: Counter-clockwise (viewed from above Earth’s North Pole)
• Solar System Mass: ~99.8% concentrated in the Sun

Note: Despite its huge mass, the Sun has only ~2% angular momentum due to its gaseous nature.

INTERNAL STRUCTURE OF THE SUN

1.  Core

• Innermost region
• Site of nuclear fusion (Hydrogen → Helium)
• Source of solar energy

2. Radiative Zone

• Energy is transferred outward by radiation
• Photons take thousands of years to escape

3.  Convective Zone

• Energy transferred by convection currents
• Hot plasma rises, cooler plasma sinks

ATMOSPHERIC LAYERS OF THE SUN

1.  Photosphere

• Visible “surface” of the Sun
• Emits most solar radiation
• Temperature: ~6000 °C
• Sunspots occur here

2.  Chromosphere

• Thin layer above the photosphere
• Temperature: ~4320 °C
• Appears reddish during solar eclipses

3.  Corona

• Outermost atmosphere
• Temperature: ~1 million °C
• Extends millions of km into space
• Source of Solar Wind
• Visible during a total solar eclipse

SUNSPOTS

• Dark patches on the photosphere
• Cooler (500–1500 °C less than surroundings)
• Caused by strong magnetic fields inhibiting convection
• Have:
  • Umbra (dark center)
  • Penumbra (lighter outer region)
• 11-year sunspot cycle
  • Solar Maximum → high sunspots
  • Solar Minimum → low sunspots
• Linked to solar storms & climate variations

SOLAR WIND

• Continuous outflow of charged particles (plasma)
• Originates from the corona
• Speed: up to 900 km/s
• Temperature: ~1 million °C
• Main components: electrons & protons

Impacts:

• Causes auroras
• Can disrupt satellites, GPS, and power grids

 PLASMA

• Fourth state of matter
• Ionised gas (free electrons + ions)
• Examples:
  • Lightning
  • Electric sparks
  • Neon lights
  • Solar wind

AURORA

• Natural light display near polar regions
• Caused when solar wind particles interact with Earth’s magnetic field & atmosphere
• Types:
  • Aurora Borealis (North)
  • Aurora Australis (South)

 SOLAR FLARES

• Sudden magnetic explosions on the Sun
• Extremely bright
• Heat corona to 10–20 million °C
• Can cause:
  • Radio blackouts
  • Satellite damage

 SOLAR PROMINENCE

• Large arc of glowing gas
• Anchored by magnetic fields
• Can extend hundreds of thousands of km
• Last for months