Redshift and blueshift are terms used to describe the shift in the wavelength of light due to the relative motion between the source of light and an observer.
Redshift: When an object emitting light is moving away from an observer, the wavelength of the light is stretched or elongated, resulting in a shift towards longer wavelengths. This shift is known as redshift because it often causes light that is originally in the visible spectrum to shift towards the red end of the spectrum. Redshift is associated with objects moving away from us and is commonly observed in the context of cosmology, such as the light from distant galaxies.
Blueshift: On the other hand, when an object emitting light is moving towards an observer, the wavelength of the light is compressed or shortened, resulting in a shift towards shorter wavelengths. This shift is known as blueshift because it often causes light that is originally in the visible spectrum to shift towards the blue end of the spectrum. Blueshift is associated with objects moving towards us and can be observed in various contexts, such as astronomical objects approaching Earth or the Doppler effect in sound waves.
The concept of redshift and blueshift is based on the Doppler effect, which is the change in frequency or wavelength of a wave due to the relative motion between the source of the wave and the observer.