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Diffractive interstellar scintillation (DISS) is scintillation (twinkling) of stars due to diffraction in the interstellar medium (ISM) rather than the familiar twinkling produced by the Earth's atmosphere. It is commonly produced by discontinuities in the ISM's ionization. When identified, DISS can sometimes be used to make very accurate measurements and images of the scintillated objects, by modeling the object and effects that could cause the observed scintillating image. The effect applies to stars but also to any such viewable-but-unresolved object, quasars in particular.
DISS effects are generally shorter-term than refractive interstellar scintillation (RISS) effects (minutes to hours for DISS versus hours to much longer for RISS), but the time-range of their effects overlap.