The Sun
G-type main-sequence star (G2V)
☼ About Our Star
The Sun is the star at the center of our Solar System, a nearly perfect sphere of hot plasma that drives the climate and weather systems on Earth and provides the energy that sustains nearly all life. Accounting for about 99.86% of the total mass of the Solar System, its immense gravitational pull keeps all eight planets, dwarf planets, asteroids, and comets in orbit.
Classified as a G-type main-sequence star (G2V), the Sun is often described as a "yellow dwarf," though its light is actually closer to white when viewed from space. It formed approximately 4.6 billion years ago from the gravitational collapse of a region within a giant molecular cloud, and it is currently about halfway through its main-sequence life.
Every second, the Sun converts roughly 600 million tonnes of hydrogen into helium through nuclear fusion in its core, releasing energy equivalent to 3.8 × 1026 watts. This energy takes about 170,000 years to travel from the core to the surface, but then only 8 minutes and 20 seconds to reach Earth as sunlight traveling at 299,792 km/s.
⚙ Structure
- Core Extends from the center to about 25% of the solar radius. Temperatures reach 15 million °C and pressure is 250 billion atmospheres — conditions under which hydrogen nuclei fuse into helium via the proton-proton chain reaction.
- Radiative Zone From 25% to about 70% of the radius. Energy produced in the core travels outward through this dense region via radiation (photon absorption and re-emission), a journey that can take over 100,000 years.
- Convective Zone The outer 30% of the Sun's interior. Here, the plasma is cool and thin enough for convection currents to carry energy to the surface, creating granulation patterns visible on the photosphere.
- Photosphere The visible "surface" of the Sun, about 500 km thick, with a temperature of ~5,500°C. This is the layer that emits the sunlight we see. Dark sunspots — regions of reduced temperature caused by magnetic flux — appear here.
- Chromosphere A thin layer above the photosphere, roughly 2,000 km deep. Temperatures rise from 4,000°C to ~20,000°C. Visible as a reddish glow during total solar eclipses, it features spicules — jets of gas shooting upward.
- Corona The Sun's outermost atmosphere, extending millions of kilometers into space. Paradoxically, it reaches temperatures of 1–3 million °C. The corona is visible as a pearly white halo during total eclipses and is the source of the solar wind.
⚡ Solar Activity
Sunspots
Temporary dark regions on the photosphere caused by intense magnetic activity. They appear in 11-year cycles and can be larger than Earth. Sunspot number correlates with overall solar activity.
Solar Flares
Sudden bursts of electromagnetic radiation from the Sun's surface, releasing energy equivalent to millions of nuclear bombs. They can disrupt radio communications and GPS signals on Earth within minutes.
Coronal Mass Ejections
Massive expulsions of plasma and magnetic field from the corona. When directed at Earth, CMEs can trigger geomagnetic storms, produce spectacular auroras, and potentially damage power grids and satellites.
Solar Wind
A continuous stream of charged particles (mostly protons and electrons) flowing outward at 400–800 km/s. The solar wind creates the heliosphere, a vast bubble that envelops the entire Solar System.
Fun Facts
- The Sun loses about 4 million tonnes of mass every second through nuclear fusion, but has enough hydrogen to keep burning for another 5 billion years.
- You could fit about 1.3 million Earths inside the Sun. If it were hollow, you could pack them in like marbles.
- Light from the Sun takes about 8 minutes and 20 seconds to reach Earth, meaning when you look at the Sun, you're seeing it as it was ~8 minutes ago.
- The Sun's gravity is so strong that even at Pluto's distance (5.9 billion km), it keeps the dwarf planet in orbit.
- The Sun rotates differentially: about 25 days at the equator but up to 36 days near the poles. This differential rotation winds up magnetic field lines and drives the solar cycle.
- In about 5 billion years, the Sun will exhaust its hydrogen fuel, swell into a red giant engulfing Mercury and Venus, then shed its outer layers to become a white dwarf about the size of Earth.