  In this paper we analyze the frequency shifts of the light emitted by
particles describing stable circular geodesics around a static black hole
immersed in an external magnetic field of arbitrary strength. This system is
represented by the Ernst solution of the Einstein-Maxwell equations. The
presence of the magnetic field and its magnitude affects both the geodesics and
the red-blueshifts of the light emitted by neutral or charged particles
orbiting the black hole. When the magnetic field is turned off we recover the
characteristic redshifts coming from particles orbiting a Schwarzschild black
hole.
