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Stellar pulsation is an oscillation of a star's structure, producing time-dependent displacements, pressure, temperature and often observable luminosity. In a radial pulsation the whole surface expands and contracts together; in more general modes, different regions move with different phases. Pressure and gravity provide restoring forces, while energy exchange determines whether a mode grows or decays.
A light curve measures brightness variations, and shifting spectral lines can track moving layers. The characteristic dynamical scale is , explaining why the mean mass density strongly influences pulsation periods, although actual periods depend on mode and stellar structure. The kappa mechanism can drive coherent oscillations in the instability strip; observed Cepheid variables then connect pulsation physics to astronomical distances.