As in terrestrial seismology, helioseismological studies of the Sun's normal modes of oscillation have done much to illuminate its global structure, internal rotation and composition. (See the article by John Harvey in PHYSICS TODAY. October 1995, page 32.) However, as with Earth, many important processes in the Sun take place on a local rather than a global scale. In terrestrial seismology, local structure is usually mapped using sound‐ray tracing techniques, in which one infers the properties of matter along the paths of sound rays from how the matter affects the rays’ arrival times. Studying the Sun's local processes is a much more complicated undertaking. In contrast to the localized earthquakes that generate Earth's seismic waves, vibrations on the Sun are excited stochastically and uniformly across the solar surface by turbulent subsurface convective flows. Moreover, solar seismic waves are evident from Earth,1.5×108km away, only as subtle Doppler shifts of spectral lines, or as slight changes in surface brightness.

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