When an ambulance approaches use we hear a higher pitch than when the ambulance moves away from us. This frequency shift has been called the Doppler Shift. The same effect occurs with star constellations. When a star constellation moves away from us we observe a lower frequency (RedShift) and we measure a higher frequency (BlueShift) when they move towards our solar system.
Based our observations on Earth of the RedShift of the Dubble Star: "Sirius" (Sirius-A and Sirius-B) Sirius-B moves away from us with 75 [km/s].
However a gravitational field also causes a "Gravitational RedShift" or "Gravitational BlueShift". Including the Gravitational RedShift of Sirius B results in the effect that Sirius B does not move away from our Solar System with 75 [km/s] but approaches our Solar System with - 5 [km/s].
Quantum Light Theory