Bottom line: A redshift reveals how an object in space (star/planet/galaxy) is moving compared to us. It lets astronomers measure a distance for the most distant (and therefore oldest) objects in our universe.
Explanation:
A redshift reveals how an object is moving in space and enables astronomers to discover otherwise-invisible planets and the movements of galaxies, and to uncover the beginnings of our universe.
They use a property called a "redshift" to describe the motion of an objects moving away from each other in space. Redshift occurs when an object emitting electromagnetic radiation recedes from an observer. The light detected appears "redder" than it should be because it is shifted toward the "red" end of the spectrum.Because the location of spectral features usually shifts to longer wavelengths -- towards the red end of the spectrum -- astronomers refer to this as the redshift of a galaxy. Take a look for yourself at the appearance of some very distant, very fast-moving galaxies in the Hubble Ultra-Deep Field .
