By James Parducci • Updated March 24, 2022
The Sun is the central star of our Solar System, a medium‑sized yellow dwarf that has been shining for over 4.5 billion years. Its intense nuclear activity powers the light and heat we depend on, and its mass governs the orbits of all the planets.
Classified as a G‑type main‑sequence star, the Sun’s surface temperature averages about 5,800 °C, while its core reaches more than 15 million °C. This classification places it among the many yellow dwarfs that populate the Milky Way, but its relative brightness and proximity make it uniquely influential for Earth.
At the heart of the Sun, hydrogen nuclei fuse to form helium, releasing energy that propagates outward as radiation. This nuclear fusion cycle sustains the Sun’s luminosity and generates the photons and particles that ultimately reach us.
Beyond visible light and heat, the Sun emits a spectrum of electromagnetic waves—including radio, ultraviolet, and X‑ray radiation. Earth’s atmosphere protects life by absorbing the most harmful wavelengths, while the remaining energy fuels photosynthesis, weather patterns, and the planet’s climate.
With a diameter of 1,392,000 km (approximately 109 times Earth's), the Sun’s mass accounts for 99.86% of the Solar System’s total mass. Its immense gravity keeps the planets in stable orbits and shapes the dynamics of the entire system.
