Redshift is a phenomenon in which the light from distant celestial objects appears to be shifted towards the red end of the spectrum. This means that the wavelength of the light is increased, and the frequency is decreased. Redshift is usually interpreted as a result of the Doppler effect, which is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. In the case of distant celestial objects, the redshift is interpreted as a result of the expansion of the universe.

As the universe expands, the distance between celestial objects increases, and the space between them is stretched. This stretching of space causes the light waves from distant objects to be stretched, resulting in a redshift. The amount of redshift is proportional to the distance of the object from the observer, so the most distant objects have the largest redshift.

Redshift is an important tool for astronomers, as it allows them to estimate the distance to distant celestial objects and to study the expansion of the universe. By measuring the redshift of galaxies and other objects, astronomers have determined that the universe is expanding at an accelerated rate, and they have developed models to explain this acceleration. Redshift has also been used to discover new exoplanets, as it can be used to detect the slight wobble in a star's motion caused by the gravitational pull of an orbiting planet.

In summary, redshift in light from distant celestial objects indicates the expansion of the universe and allows astronomers to study the universe and discover new celestial objects.