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:
Furthermore, characteristics of the star may be determined, including radius, mass, Metallicity (Z) 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.
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:
Wide Field Infrared Explorer (WIRE)