When a vibrating object is moving blank and observer, the measured frequency of vibrations will be higher than if the observer and object were stationary relative to each other when a star is moving away from the observer on earth, the lights spectrum of the star will appear blank compared to the light spectrum of the sun, which is considered to be its earths frame of reference
When a vibrating object is moving towards an observer, the measured frequency of vibrations will be higher than if the observer and object were stationary relative to each other.
When a star is moving away from the observer on Earth, the light spectrum of the star will appear shifted towards the red end of the spectrum compared to the light spectrum of the Sun, which is considered to be its Earth's frame of reference. This is known as the redshift phenomenon and is due to the Doppler effect.