Frequency separation is a term used in Helio

Helioseismology

Helioseismology is the study of the propagation of wave oscillations, particularly acoustic pressure waves, in the Sun. Unlike seismic waves on Earth, solar waves have practically no shear component . Solar pressure waves are believed to be generated by the turbulence in the convection zone near...

 and Asteroseismology

Asteroseismology

Asteroseismology also known as stellar seismology is the science that studies the internal structure of pulsating stars by the interpretation of their frequency spectra. Different oscillation modes penetrate to different depths inside the star...

 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.

A further frequency separation, the rotational splitting can be seen in high-resolution solar data between modes of the same angular degree, but different azimuthal order (m). This gives information

Star	Large Frequency Separation	Small Frequency Separation
The Sun Sun The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...	136 μHz	9.0 μHz
Arcturus	0.825 0.049 μHz	Not Present