Asteroseismology is the seismology of stars. Helioseismology (Solar Seismology) is specifically the seismology of the sun.
Study of the spectra of vibration of the Sun and other stars reveals information about their structure. Vibrations are divided into three types (Pulsation Modes):
Stars also can exhibit Radial Modes of vibration: compression and decompression as happens when air resonances in a pipe.
Furthermore, characteristics of the star may be determined, including radius, mass, Metallicity and age. This is done by creating stellar models that include the resulting oscillation, and by comparing a star's asteroseismological characteristics with that of stars with known radius, mass, etc. Stellar Radius Determination by asteroseismology is considered more accurate than other methods usable at similar distances: it is thought to be accurate to about 2-to-3 percent. Sound speeds within stellar material can be estimated with enough accuracy to help determine radius from the resonances apparent in the vibrations.
The Acoustic Frequency (time for a p-mode to travel its Wavelength) depends upon the state of the material, and thus generally varies with the distance from the center of the star.
Spacecrafts to study asteroseismology include:
Stellar Radius Determination
Wide Field Infrared Explorer (WIRE)