The Sun

The Sun is a G-type main-sequence star (G2V) that fuses hydrogen into helium in its core, releasing the energy that powers Earth's climate, weather, and life. It contains 99.86% of the solar system's mass.

Every atom in your body was forged in stars, but the Sun is the star that made Earth habitable. Understanding solar physics explains climate, space weather, and the ultimate fate of our planetary system.

The Sun's core reaches 15 million K, where proton-proton fusion converts hydrogen to helium via E=mc². Energy takes ~100,000 years to diffuse outward, then radiates from the 5,800 K photosphere. The chromosphere and corona extend millions of km; the corona is paradoxically hotter than the surface — a major unsolved problem.

Ancient cultures worshipped the Sun as a deity. Galileo's telescopic sunspots (1610) proved the Sun rotates. In the 20th century, we learned stars are fusion engines; neutrinos from the core confirmed the proton-proton chain (Homestake, Super-Kamiokande).

Peel the Sun like an onion: core (fusion), radiative zone, convective zone, photosphere, chromosphere, corona. Sunspots mark cooler magnetic regions; solar flares and CMEs blast particles across the solar system.