Structure of the Sun

The Sun

• The Sun is a huge star, a glowing ball of extremely hot gas called plasma. Plasma is gas in which atoms are stripped of electrons, making it electrically charged.
• It is so big that 109 Earths could fit side by side across its diameter, and it could hold 1.3 million Earths in its volume.
• The Sun is made mostly of hydrogen (~73%) and helium (~25%). The remaining 2% are other elements like carbon, oxygen, and nitrogen, which are important for life on Earth.
• Unlike Earth, the Sun has no solid surface or core—everything is a hot, glowing gas.
• The Sun rotates in a counter-clockwise direction (if viewed from above Earth’s north pole). Different parts rotate at different speeds:
  
  • Equator: ~24 days
  • Poles: ~30+ days
  • Average rotation: ~27 days

Internal Structure of the Sun

1. Core
   
   • The center of the Sun, about 20% of the Sun’s radius.
   • Temperature: ~15 million °C.
   • Here, nuclear fusion happens: hydrogen atoms combine to form helium, releasing huge amounts of energy. This energy is what powers the Sun and produces sunlight.
2. Radiative Zone
   
   • Surrounds the core, extending from 25% to 70% of the Sun’s radius.
   • Energy moves slowly as light (photons), because the dense gas keeps scattering them.
3. Convective Zone
   
   • Outermost layer of the Sun’s interior, about 200,000 km thick.
   • Energy moves through convection: hot gas rises to the surface, cools, and sinks back down, similar to a boiling pot of oatmeal.

Sun’s Atmosphere

1. Photosphere
   
   • The visible surface of the Sun that we can see with telescopes.
   • Temperature: ~6,000 °C
   • Most sunlight comes from this layer.
   • The surface is uneven and has sunspots (cooler, darker areas caused by strong magnetic fields).
2. Chromosphere
   
   • A thin layer above the photosphere, 3,000–5,000 km thick.
   • Temperature: ~10,000 K
   • Appears red during a total solar eclipse.
3. Transition Region
   
   • A tiny layer where the temperature rises rapidly from 10,000 K to 1 million K.
4. Corona
   
   • The Sun’s outer atmosphere, extending millions of kilometers into space.
   • Temperature: 1–2 million K
   • Source of the solar wind (stream of charged particles).
   • Visible during a total solar eclipse as a white glowing halo.

Sun’s Phenomena

1. Sunspots
   
   • Dark, cooler patches on the photosphere.
   • They form where the magnetic field is extremely strong, trapping heat.
   • Sunspots have a dark umbra (center) and a lighter penumbra (edge).
2. Solar Flares
   
   • Sudden bursts of energy near sunspots.
   • Heat the corona to 10–20 million °C.
   • Can disrupt satellites, radio signals, and power grids on Earth.
3. Solar Prominences
   
   • Huge arcs of glowing gas extending from the Sun’s surface.
   • Held by magnetic fields.
   • Can last months and sometimes erupt, sending solar material into space.
4. Coronal Holes
   
   • Darker, cooler areas in the corona where the Sun’s magnetic field is open.
   • Solar wind escapes faster from these regions.
   • Can last weeks to months, longer during the solar minimum.
     
     
5. Solar Wind
   
   • Stream of charged particles (electrons and protons) flowing outward from the Sun at up to 900 km/s.
   • When they interact with Earth’s magnetic field, they create auroras:
     
     • Aurora Borealis (Northern Lights)
     • Aurora Australis (Southern Lights)

Plasma

• Plasma is a state of matter like solid, liquid, and gas.
• It’s made of ionized gas (atoms stripped of electrons).
• Examples: lightning, neon lights, and the Sun itself.

Why the Sun Matters

• Provides light and heat, making life on Earth possible.
• Drives space weather that affects satellites and astronauts.
• Causes geomagnetic storms and auroras through solar wind and flares.
• Coronal holes and solar winds affect conditions in space that our technology and astronauts travel through.