The Seismic Structure of the Sund

{ GONG data reveal that the internal structure of the Sun can be well represented by a calibrated standard model. However, immediately beneath the convection zone and at the edge of the energy-generating core the sound-speed variation is somewhat smoother in the Sun than it is in the model. This could be a consequence of chemical inhomogeneity being too severe in the model, owing perhaps to inaccurate modelling of gravitational settling or to neglected macroscopic motion that may be present in the Sun. Accurate knowledge of the Sun's structure enables inferences to be made about the physics that controls the Sun, for example through the opacity, the equation of state or wave motion. Those inferences can then be used elsewhere in astrophysics.