Our Star: The Sun
The Sun is a G-type main-sequence star, a nearly perfect sphere of hot plasma, whose gravity holds the solar system together.
Layers of the Sun
Interior Layers:
1.Core: The innermost region where energy is generated by nuclear fusion. Temperatures reach about 15 million K.
2.Radiative Zone: A dense region surrounding the core where energy is transported outwards by photons of light. It can take a photon over 100,000 years to pass through this zone.
3.Convective Zone: The outermost layer of the interior. Energy is transported by the physical movement of hot gas in convection cells, similar to boiling water.
Atmospheric Layers:
1.Photosphere: The visible 'surface' of the Sun that we see.
2.Chromosphere: A reddish layer of gas above the photosphere.
3.Corona: The Sun's vast, tenuous outer atmosphere, visible during a total solar eclipse. It is extremely hot, reaching temperatures of over a million K.
Energy Production: The Proton-Proton Chain
The Sun produces energy by fusing hydrogen into helium in its core via a process called the proton-proton (p-p) chain.
Overall Reaction: 4 ¹H → ⁴He + 2 e⁺ + 2 ν + energy
(Four hydrogen nuclei fuse to form one helium nucleus, two positrons, two neutrinos, and a great deal of energy in the form of gamma rays).
This process converts a small amount of mass into energy according to E=mc².
Solar Activity
The Sun's magnetic field is highly dynamic and drives several phenomena known as solar activity.
Sunspots: Dark, cooler regions on the photosphere where intense magnetic fields have emerged from the interior, inhibiting convection. They appear in an approximately 11-year cycle.
Solar Flares: Sudden, intense bursts of radiation and energy from the Sun's surface, often near sunspots.
Coronal Mass Ejections (CMEs): Massive eruptions of plasma and magnetic field from the Sun's corona. If directed towards Earth, they can disrupt satellites, power grids, and cause brilliant auroras.