Our Sun, a colossal sphere of hot plasma, radiates immense energy that sustains life on Earth and influences our solar system. While appearing as a uniform disk, it has distinct layers. Understanding these layers helps scientists unravel how the Sun generates its energy and continuously showers our planet with light and heat.
The Sun’s Internal Structure
Deep within the Sun, immense pressure and extreme temperatures forge its internal structure, comprising three primary layers.
The Core
The core extends to about 20-25% of the Sun’s radius. Temperatures reach approximately 15 million Kelvin, and densities can be 150 grams per cubic centimeter. Here, nuclear fusion of hydrogen into helium releases the vast energy that powers the Sun.
The Radiative Zone
The radiative zone surrounds the core, spanning from roughly 25% to 70% of the Sun’s radius. In this dense region, energy travels outward through the repeated absorption and re-emission of photons. Photons can take over 170,000 years to traverse this zone due to constant interactions with the packed matter. This slow process moves energy from the core.
The Convective Zone
The convective zone is the outermost internal layer, extending from about 70% of the radius to near the Sun’s visible surface. Here, cooler, less dense plasma allows for energy transport through convection. Hot plasma rises, cools, and sinks, similar to boiling water, creating giant convection currents that carry heat outward. This turbulent motion is the final stage of energy transport within the Sun’s interior.
The Sun’s Atmospheric Layers
Beyond its interior, the Sun possesses a dynamic atmosphere composed of three distinct layers, each with unique characteristics and observable phenomena.
The Photosphere
The photosphere is the visible “surface” of the Sun, from which most light escapes into space. This layer, about 500 kilometers thick, has a temperature of approximately 5,500 degrees Celsius. It is characterized by sunspots, cooler, darker areas caused by intense magnetic fields. The photosphere’s grainy appearance, known as granulation, results from underlying convective currents.
The Chromosphere
Above the photosphere is the chromosphere, a reddish layer primarily visible during total solar eclipses when the brighter photosphere is obscured. This layer extends about 2,000 kilometers, with temperature increasing with altitude to 400,000 degrees Celsius at its top. Spicules (jets of gas) and solar flares (sudden bursts of radiation) originate in this active region.
The Corona
The corona is the outermost atmospheric layer, a vast, extremely hot halo of plasma extending millions of kilometers into space. Only during a total solar eclipse can it be seen with the naked eye, appearing as a pearly white crown. Its temperature can reach millions of Kelvin, and it is the source of the solar wind, a continuous stream of charged particles flowing outward through the solar system.
Why the Sun Has Layers and How We Know
The Sun’s layered structure, consisting of six primary regions—the core, radiative zone, convective zone, photosphere, chromosphere, and corona—arises from fundamental differences in temperature, density, pressure, and energy transfer methods. Each layer represents a distinct physical environment where conditions dictate how energy is generated and transported from the Sun’s interior to its outer atmosphere.
Scientists employ sophisticated techniques to study these otherwise inaccessible layers. Helioseismology, analogous to seismology on Earth, involves analyzing the sound waves that travel through the Sun’s interior. By observing the patterns of these waves on the Sun’s surface, researchers can infer details about the temperature, density, and composition of the internal layers.
Spectral analysis of light from different parts of the Sun provides information about its atmospheric layers. By examining the wavelengths of light absorbed or emitted by various elements, scientists can determine the temperature, chemical composition, and motion within the photosphere, chromosphere, and corona. These methods allow for a comprehensive understanding of the Sun’s complex, layered organization.