The Sun is the star that anchors the Solar System. It is a nearly spherical, luminous ball of hot plasma whose gravity governs the orbits of planets, dwarf planets, comets and asteroids. By producing light and heat through nuclear fusion in its core, the Sun is the primary energy source for Earth’s climate and ecosystems.

Structure and composition

The Sun is composed mostly of hydrogen and helium. Its internal structure is commonly divided into the core (where fusion converts hydrogen into helium), the radiative and convective zones, and the visible atmosphere made of the photosphere, chromosphere and the outer corona. Magnetic fields thread these layers and drive much of the Sun’s complex behavior.

Solar activity and space weather

Magnetic activity creates sunspots, solar flares and coronal mass ejections (CMEs). These phenomena modulate the solar wind — a continuous flow of charged particles that inflates the heliosphere. Strong eruptions can produce auroras, disrupt radio communications, affect satellites, and, in extreme cases, damage electrical infrastructure on Earth.

Key features

  • Sunspots: cooler, magnetically active regions on the photosphere.
  • Solar cycle: an approximately 11-year variation in magnetic activity.
  • Heliosphere: the magnetic bubble carved out by the solar wind around the Solar System.

Scientists observe the Sun from ground-based solar telescopes and space missions to avoid atmospheric distortion and study high-energy processes. Notable spacecraft have provided detailed views of the corona, solar wind and magnetic fields, improving space-weather forecasting.

Importance and future

The Sun sustains life on Earth, drives weather and ocean currents, and enables technologies like solar power. It is a middle-aged G-type main-sequence star; after several billion more years its fuel supply will change, leading to expansion into a red giant and eventual contraction to a white dwarf. Understanding the Sun remains essential for predicting long-term climate trends and protecting technological society from solar storms.