Knowra Photosphere Photosphere A star’s visible outer layer, from which most of its observed light escapes. Its apparent surface marks the depth where the gas becomes transparent enough for photons to travel freely into space.
Stellar atmosphere : The outer gaseous layers of a star, including regions above and below its visible surface. The photosphere is the deepest visible layer within this broader atmospheric structure.
Stellar structure : The internal organization and physical balance of a star from its core to its outer layers. The photosphere is the outer boundary condition for models of a star’s structure.
Solar spectroscopy : The analysis of the Sun’s light by wavelength to infer physical properties of its atmosphere. Photospheric spectral lines reveal elemental abundances, temperatures, and line-of-sight motions.
Chromosphere : A thin atmospheric layer above a star’s photosphere, where temperature generally rises outward. It lies above the visible surface and becomes prominent in selected spectral lines.
Optical depth : A measure of how much radiation is absorbed or scattered while traveling through a medium. The photosphere is conventionally located near optical depth one.
Convection zone : A stellar region where energy is transported mainly by moving parcels of hot and cool gas. In the Sun, convection below the photosphere drives the visible granulation.
Doppler imaging : A method that maps stellar surface features using rotationally shifted spectral lines. Photospheric absorption lines can trace spots and other surface inhomogeneities.
Solar corona : The Sun’s extremely hot, tenuous outer atmosphere, extending far beyond its visible disk. Unlike the photosphere, the corona is faint in visible light and usually requires special viewing conditions.
Radiative transfer : The propagation of radiation through matter by absorption, emission, and scattering. It determines which layers contribute the light escaping from the photosphere.
Plasma : An ionized gas containing free charged particles that respond collectively to electromagnetic fields. Photospheric matter is mostly plasma, though its outer layers are only partly ionized.
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