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gravitational redshift(Einstein shift) The redshift of spectral lines that occurs when radiation, including light, is emitted from a massive body. In order to ‘climb out’ of the body's gravitational field, the radiation must lose energy. The radiation frequency must therefore decrease and its wavelength λ, shift by δλ toward a greater value. The redshift is given by
G is the gravitational constant, m and r the mass and radius of the massive body, and c is the speed of light. Gravitational redshift was predicted by Einstein's general theory of relativity and although extremely small has been detected, for example, in the spectra of the Sun and several white dwarfs. The redshift of the Earth's gravitational field has been determined very accurately using beams of radiation traveling upward through a tall building. Predicted and measured values agree very closely.