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Seismology of the Sun, Stars, and Giant Planets
The Sun and many stars ring like a bell, as they are filled with acoustic waves excited by turbulent convection (see animation on right). These waves can be used to “see” into the solar interior using a technique called helioseismology. A useful analogy is Earth seismology. When an earthquake occurs, acoustic “sound” waves generated at the source travel deep into the Earth's interior and refract back towards the surface, where they are subsequently measured by seismographs. Comparisons of the observed travel times and amplitudes of the waves with theoretical models of the expected values allow geophysicists to infer sub-surface properties.
The situation is very similar in the case of the Sun. Waves are continuously excited and travel throughout the solar interior, some even all the way to the core. They then are refracted back to the surface where they can be measured using ground- and space-based telescopes. The information in the waves tells us about flows, sound speed, chemical abundances, asphericity, and magnetic fields along the areas where the waves travelled. Helioseismology has given us fascinating insights about the structure of the Sun.