An Etymological Dictionary of Astronomy and Astrophysics
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Any frequency of small-amplitude oscillation for a system with a position of stable equilibrium and in the absence of external forces. In other words, the frequency of → free oscillation. Also called characteristic frequency.

→ natural; → frequency.

The highest frequency that can be determined in a Fourier analysis of a discrete sampling of data.

→ Nyquist formula; → frequency.

The natural frequency at which internal oscillations of a plasma occur. The plasma frequency is proportional to the square root of the electron density. → plasma oscillation.

→ plasma; → frequency.

The frequency at which an oscillation is intermittently quenched, as in a super-regenerative receiver.

→ quench; → frequency.

The → electromagnetic radiation with the frequency range between 3 → kiloherz (kHz) to 300 → gigahertz (GHz). See also → radio wave.

→ radio; → frequency.

Statistics: The number of the occurrences of an event divided by the number of observations.

→ relative; → frequency.

The frequency at which a system is in → resonance.

→ resonance; → frequency.

1) The number of rotations per unit time of a rotating object.
2) The number of → stellar rotations per unit time. The reciprocal of the → rotation period. This parameter usually refers to the equator of the star, because stars do not rotate as solid bodies.

→ rotation; → frequency.

The revolution frequency of a → relativistic particle of charge q and mass m in the → uniform magnetic field B of a synchrotron. It is expressed by: f_syn = qB/2πγm, where γ is the → Lorentz factor. This frequency is lower than → cyclotron frequency for a → non-relativistic case.

→ synchrotron; → frequency.

The frequency at which the atoms in a molecule vibrate. The frequencies of → molecular vibrations in diatomic molecules are in the order of 10^-12 to 10^-14 Hz. In such molecules, the only → vibrational mode available is along the bond. More complicated molecules have many types of vibration and stretching modes.

→ vibrational; → frequency.