The Sun as a Star

The Sun is a star that appears unique only because it is close enough for its surface to dominate the sky. It sits in the top 10 % of stars by size; most stars are smaller red dwarfs. By mass it outweighs the entire solar system, acting as the gravitational anchor for all planets.

Internal Structure and Energy

The Sun is a sphere of hydrogen gas about 1.4 million km in diameter. At its core the temperature reaches 15 million °C and the pressure is 260 billion times Earth’s atmospheric pressure. Hydrogen atoms are stripped of electrons, allowing protons to fuse into helium and release energy according to (E=mc^2). Every second, 700 million tons of hydrogen become 695 million tons of helium, converting 5 million tons of mass into radiant energy. That energy drifts outward for 100 000–200 000 years before emerging at the surface.

Solar Surface and Atmosphere

Convection carries heat upward: hot gas rises in columns, cools, and sinks back, forming a continuous churn. The photosphere is the thin, transparent layer where photons finally escape into space. Above it lies the corona, an extremely tenuous atmosphere that is paradoxically hotter—exceeding 1 million °C. The corona expands into the solar wind, a stream of charged particles that races outward at roughly 1 million km/h.

Magnetic Activity and Solar Phenomena

The Sun’s plasma is electrically charged, so its motion generates magnetic fields. When magnetic field lines tangle, they inhibit plasma from sinking, producing cooler, darker sunspots. Bright faculae rim these spots and can raise the Sun’s total output. Large arcs of plasma that follow magnetic loops appear as prominences or filaments. When tightly wound magnetic lines snap, they unleash solar flares—intense, localized explosions. A coronal mass ejection (CME) is a far larger eruption, hurling billions of tons of material into space. As one speaker put it, “If a flare is like a tornado—intense and localized—a CME is like a hurricane, huge and strong.”

Impact on Earth

Solar particles guided by Earth’s magnetic field create auroras near the poles. Powerful solar storms can induce electric currents in the planet’s crust, threatening power grids and satellites. The 1859 storm, the most energetic recorded, and a near‑miss in 2012 illustrate the potential for disruption. In 1989, a solar storm knocked out power across Quebec, demonstrating the real‑world stakes of space weather.