An Etymological Dictionary of Astronomy and Astrophysics

1. The resolution of white light into its component wavelengths, either by → refraction or by → diffraction.
   Dispersion is actually an effect in which radiations having → different wavelengths travel at different speeds in the medium. Since the → angle of refraction of each radiation vary as a function of its → wavelength, the component waves deviate from each other.
   

2. The rate of change of → refractive index with wavelength: dn/dλ. → Cauchy’s equation shows that dispersion varies approximately as the inverse cube of the wavelength.
   

3. The selective → retardation of → radio waves when they propagate through a → plasma. As a result, higher → frequency waves from a → pulsar will arrive at the Earth before the lower frequencies due to the presence of → intervening → ionized gas in the → interstellar medium.
   → dispersion measure.
   

4. Statistics: The spread of values of a → variable around the → mean or → median of a → distribution.

See also: Verbal noun of → disperse.