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Scintillations of radio waves are observed to occur because of irregularities in the refractive index of the ionosphere, the interplanetary medium, and the interstellar medium giving ionospheric scintillation, interplanetary scintillation (IPS), and interstellar scintillation (ISS), respectively. IPS may be used in determining the angular sizes of radio sources at meter wavelengths in the range 0.1 to 2 arc seconds, or for measuring parameters of the solar wind. ISS cause some of the random fluctuations in the intensity of pulses received from pulsars.
Light may be deflected from its direction of travel by fine particles of solid, gaseous, or liquid matter. For very small particles (less than one wavelength in size) the effect results from diffraction, reflection playing a more important part with increasing size; this is known as Rayleigh scattering and is very dependent on wavelength. Very small particles scatter blue light more strongly than red light. This leads to the reddening of starlight by cosmic dust and to the reddening of the Sun when seen through a thick layer of atmospheric dust.