specific region of the solar interior, known as a cavity, and its frequency is sensitive to properties, such as temperature and mean molecular weight, of the solar material in the cavity. The sound waves can be considered as damped harmonic oscillators as they are stochastically excited and intrinsically damped by turbulent convection in the outer approximately 30per cent by radius of the solar interior. The strongest p-mode oscillations have a periodicity of approximately 5minutes. The solar oscillations can be observed in two ways: by line-of-sight Doppler velocity measurements over the visible disk; or by measuring the variations in the continuum intensity of radiation, which are caused by the compression of the radiating gas by the waves.

The horizontal structure of p modes can be modeled as spherical harmonics and so can be described by three main components: Harmonic degree, $l$, which indicates the number of node lines on the surface; azimuthal degree, $m$, which describes the number of planes slicing through the equator and takes values between $-l\le m\le l$; and radial degree, $n$, which gives the number of radial nodes in the solar interior. If the Sun was completely spherically symmetric the frequencies of the oscillations would be degenerate 