JILA, Univ. of Colorado, Boulder, CO 80309
The sun is oscillating in an intricate though gentle manner. The patterns of motion observed in the solar atmosphere are complicated, for they result from interference between about 10[sup 7] resonant modes of oscillation of the interior. The sun possesses both acoustic p modes, for which pressure is the restoring force, and gravity g modes, for which buoyancy is the dominant force. Each resonant mode resides in a cavity beneath the solar surface, the depth of which depends both on the type of mode and on its geometry. Some cavities are quite shallow, whereas others extend to the very center of the star. Since the frequencies of the modes are determined by the stratification and dynamics of the portion of the sun where their amplitudes are appreciable, accurate determination of the frequencies by observations affords remarkable ways of probing the inside of the star. During the past decade there has been significant progress in both observation and theory. The unravelling of information from many modes forms the basis of the subject called helioseismology. It promises study of the inside of the sun in sufficient detail to test the premises of stellar structure theory, and thus has implications for much of astrophysics. It can also provide crucial information about the temperature and mass distribution within the sun for testing issues in particle physics and theories of gravitation.