Stellar atmosphere
A star’s outer layers from which observable radiation emerges, including the photosphere and, in many stars, the chromosphere and corona.
Photosphere: The visible layer of a star from which most of its observed light escapes. It is the deepest atmospheric layer directly observed in most stars.
Radiative transfer: The propagation of radiation through matter, including its absorption, emission, and scattering. It governs how photons travel through atmospheric layers before escaping.
Stellar classification: The grouping of stars by spectral properties, especially temperature and spectral features. Spectral lines formed in stellar atmospheres help assign stars to spectral classes.
Blackbody radiation: Electromagnetic radiation with a spectrum determined solely by the temperature of an ideal absorber and emitter. Real stellar spectra depart from a blackbody because atmospheric matter absorbs and emits at selected wavelengths.
Chromosphere: A thin atmospheric layer above a star’s photosphere, often visible in specific spectral lines. It lies above the photosphere and reveals temperature and activity structure.
Hydrostatic equilibrium: A balance between pressure gradients and gravity in a stationary fluid. It describes how pressure supports much of a star’s atmosphere against gravity.
Abundance analysis: The determination of chemical element abundances from observed astronomical spectra. Atmospheric absorption lines provide evidence for a star’s chemical composition.
Solar atmosphere: The outer layers of the Sun, including its photosphere, chromosphere, and corona. It is the best-resolved example of a stellar atmosphere, though not representative of every star.
Stellar corona: The tenuous, extremely hot outer atmosphere surrounding a star. It is the outermost atmospheric layer in stars with an extended corona.
Stellar opacity: A measure of how strongly stellar material impedes the passage of radiation. Opacity controls where radiation is absorbed and how energy moves through the atmosphere.