Final answer:
The light of a source appears redder when it is moving away from the observer due to the Doppler effect.
Step-by-step explanation:
In physics, this phenomenon is known as the Doppler effect. The Doppler effect refers to the change in frequency or wavelength of a wave due to the relative motion between the source of the wave and the observer.
In the case of light, when a source is moving away from the observer, its light appears redder than it actually is. This is because the wavelength of the light waves is stretched or lengthened, causing a shift towards the red end of the spectrum. This is known as a redshift.
On the other hand, when a source of light is moving towards the observer, its light appears bluer than it actually is. This is because the wavelength of the light waves is compressed or shortened, causing a shift towards the blue end of the spectrum. This is known as a blueshift.
Complete Question:
In the case of light, when a source is moving away, its light appears redder than it actually is___________