Solar Structure: Observation, Measurement & Evidence

The core occupies the central region where temperature and density permit nuclear fusion. Energy then moves outward through the radiative zone and convective zone before escaping from the photosphere. Above the visible surface, the chromosphere and transition region lead into the tenuous million-degree corona.

Solar models are constrained by the Sun's mass, radius, luminosity, composition, spectrum, and age. Helioseismology probes internal sound-speed structure, while spectroscopy identifies atmospheric composition and temperature. Imaging at different wavelengths isolates features in the photosphere, chromosphere, and corona.

Gravity compresses the solar interior while gas and radiation pressure resist collapse, producing hydrostatic equilibrium. In the radiative zone photons exchange energy repeatedly with matter, while in the convective zone bulk plasma motions carry energy outward. Temperature, density, pressure, and ionization change strongly with radius.

Helioseismology uses solar oscillation frequencies to reconstruct internal sound speed and rotation, while neutrinos probe nuclear reactions directly. Spectroscopy measures photospheric composition and atmospheric temperature, and imaging at different wavelengths isolates chromospheric and coronal layers. These independent measurements broadly agree with standard solar models.