Question

check: 1. what is redshift and blueshift?

Explanation:

Redshift and blueshift are terms in astronomy related to the Doppler - effect for light. Redshift occurs when an object is moving away from an observer, causing the light's wavelength to stretch and shift towards the red - end of the spectrum. Blueshift happens when an object is moving towards an observer, making the light's wavelength compress and shift towards the blue - end of the spectrum.

Answer:

Redshift is the shift of light's wavelength towards the red - end of the spectrum when an object is moving away from an observer. Blueshift is the shift of light's wavelength towards the blue - end of the spectrum when an object is moving towards an observer.