Redshift is a phenomenon in which the light from an object appears to be shifted towards the red end of the spectrum. This means that the wavelength of the light is longer than it would be if the object were stationary.

Redshift is an important tool for astronomers because it can be used to measure the distance to other galaxies. The further away a galaxy is, the greater its redshift.

Red shift tells us that:

- The universe is expanding, and the galaxies are moving away from us. The greater the red shift, the faster the galaxy is moving away.

- The expansion of the universe is accelerating. This is because the red shift of galaxies is getting larger and larger as time goes on.

- The universe is about 13.8 billion years old. This is based on measurements of the red shift of the most distant galaxies.