Diffraction has a number of consequences for astronomy. Two of the more important are that this property is the basis for the diffraction grating that can be used to separate light into its constituent colors, and that diffractive effects set an absolute limit on the quality of an image observed through an optical instrument such as a telescope.

This diffractive limit occurs because the lenses of such objects are of finite size and diffract light because they cut off part of the light wave.