 By Birkhoff's theorem, such a field is described in general relativity by the Schwarzschild metric, formula_3, where formula_4 is the clock time of an observer at distance "R" from the center, formula_5 is the time measured by an observer at infinity, formula_6 is the Schwarzschild radius formula_7, "..." represents terms that vanish if the observer is at rest, formula_8 is Newton's gravitational constant, formula_9 the mass of the gravitating body, and formula_10 the speed of light.The result is that frequencies and wavelengths are shifted according to the ratio

where 

This can be related to the redshift parameter conventionally defined as formula_15.In the case where neither the emitter nor the observer is at infinity, the transitivity of Doppler shifts allows us to generalize the result to formula_16.