Frequency separation

Frequency separation is a term used in Helio and Asteroseismology for the spacing in frequency between adjacent modes of oscillation having the same angular degree (l) but different radial order (n).

For a Sun-like star the frequency can be further described using the 'large frequency spacing' between modes of different radial order (136 μHz in the Sun), and the 'small frequency spacing' between modes of even and odd angular degree within the same radial order (9.0 μHz in the Sun). The period corresponding to the large frequency spacing can be shown to be approximately the same as the time required for a sound wave to travel to the centre of the Sun and return, confirming the global nature of the oscillations seen.