Doppler equation Slight shifts in the color of light coming from a distant star can clue astronomers in to an orbiting planet via the Doppler equation, which links changes in the wavelength (A.) of light to the motion (v) of the thing emitting it. As a star approaches, its light is compressed and looks bluer; as it moves away, the light stretches and reddens. An unseen planet that tugs the star back and forth will yield a characteristic pattern of color changes. Closer to home, the Doppler equation helps enforce speed limits and predict weather by measuring the speed of cars and storm systems; Doppler shifts also alter radio signals from communications satellites in ways that must be canceled out.
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