In recent years, another method of study, helioseismology, has been developed to determine internal conditions in the Sun. The Sun is vibrating with a complex spectrum of frequencies, due to the propagation of resonant sound waves through its outer layers. These solar oscillations are the product of the Sun's internal structure in the same fashion that the vibrations of a drum are related to the drum's physical structure. Helioseismology has confirmed predictions of the depth of the outer convective layer made by the Standard Solar Model.