The Sun is a massive, self-luminous sphere of hot gas containing over 99.8% of the entire solar system’s mass. It continuously radiates energy equivalent to trillions of nuclear bombs every second. This immense power source results from its unique composition and internal structure, which generate light and heat through nuclear processes. Understanding the Sun’s makeup is essential to appreciating its role as the source of energy for our planet.
The Primary Chemical Ingredients
The Sun’s composition is dominated by the lightest elements, typical of most stars. By mass, approximately 73% of the Sun consists of Hydrogen, which serves as the star’s primary fuel source. Helium is the second most abundant element, accounting for roughly 25% of the total mass. Together, these two elements make up about 98% of the Sun’s material content.
The remaining 2% of the Sun’s mass is composed of all other elements, which astronomers collectively refer to as “metals.” The most abundant of these heavier elements include Oxygen, Carbon, Neon, and Iron. Oxygen is the most common metal (about 0.77% of the mass), followed by Carbon (approximately 0.29%). Although they constitute a small fraction, these elements are important for the star’s energy transfer and analysis.
Plasma: The Dominant State of Matter
The high temperatures and immense pressures throughout the Sun prevent its components from existing as solid, liquid, or gas. Instead, the Sun is a nearly perfect sphere of plasma, often called the fourth state of matter. Plasma is an ionized gas where extreme thermal energy strips electrons away from atomic nuclei. This creates a superheated mixture of free electrons and positively charged ions.
The electrical charge of plasma makes it highly responsive to magnetic fields, leading to the Sun’s dynamic magnetic activity. Plasma is an excellent electrical conductor, facilitating the generation of the star’s powerful magnetic field through the movement of charged particles. The constant motion of this superheated plasma is responsible for all observed solar phenomena, including solar flares and sunspots.
The Sun’s Internal Architecture
Energy is generated and transported through three distinct internal zones beneath the visible surface. At the center is the core, where the temperature reaches about 15 million Kelvin and pressure is at its peak. This extreme environment allows for nuclear fusion, where Hydrogen nuclei combine to form Helium nuclei via the proton-proton chain. This fusion process releases enormous amounts of energy, primarily as high-energy gamma-ray photons.
Surrounding the core is the radiative zone, extending outward to about 70% of the solar radius. In this dense layer, energy is transported as photons repeatedly collide with charged particles, being absorbed and re-emitted. Due to the high density, a single photon can take hundreds of thousands of years to migrate through this zone. The radiative zone acts as a thermal insulator, helping maintain the high temperature required for fusion.
The outermost internal layer is the convective zone, which is about 200,000 kilometers deep. Here, the temperature is low enough that energy transfer by radiation becomes inefficient compared to the movement of matter. Hot plasma rises toward the surface, cools, and then sinks back down, creating enormous circulation patterns called convection cells. This convective motion efficiently carries energy to the star’s outer boundary.
The Observable Solar Atmosphere
The energy that has journeyed through the Sun’s interior finally escapes into space through the observable solar atmosphere, which is composed of three main layers. The innermost layer is the photosphere, which is perceived as the Sun’s visible “surface.” This thin layer, roughly 500 kilometers thick, is where the plasma becomes transparent enough for photons to escape, and its temperature is approximately 5,800 Kelvin. The photosphere exhibits a mottled appearance called granulation (the tops of convection cells) along with cooler, darker regions known as sunspots.
Above the photosphere lies the chromosphere, a layer only visible during a total solar eclipse. This layer is characterized by a reddish glow, primarily due to the emission of light from excited hydrogen atoms. The temperature in the chromosphere begins to increase with altitude, reaching about 10,000 Kelvin at its outer edge.
The corona is the Sun’s superheated, tenuous outermost atmosphere, extending millions of miles into space. The temperature in the corona soars to several million Kelvin, which remains a major unsolved puzzle in solar physics. This extremely hot plasma streams away from the Sun through regions called coronal holes, forming the solar wind. The solar wind is a continuous flow of charged particles that travels throughout the solar system.