Light interference, due to light interaction with an physical edge. The size of the edge must be the same as the light wavelength in order to produce the interference. Astronomers observe light in specific wavelengths with a diffraction grating, a glass surface with fine grooves cut into it. The groove dimensions correspond to wavelengths of light, around 500 nanometers (green) +/- 150 nanometers (blue to red). Astronomers use the grating to "spread" light into its component colors, to learn about a star's temperature, composition, speed, and distance from Earth. 


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