A Mystery of Space: S T A R S- [Redshift] U12

     To know how redshift works, we will first explain how light is affected by the direction an object is moving, and what light it produces.
     Light travels in waves, and the color of light depends upon the wavelength (the length between each wave (trough to trough, or crest to crest, to be more specific)). Waves of blue light are much closer together than waves of red light. If a very fast moving object is sending out light, the light waves will be closer the direction it is moving, but stretched out in the opposite direction. This means that light from an approaching object would seem blue, and light from an object moving away would seem red. This means that an object moving away from Earth looks red, and an object coming closer to Earth looks blue. When the color of an object is changed from moving away, this is called redshift.
     Distant galaxies are moving away from Earth at thousands of miles per second. Their light waves are stretched by this speed, making them look redder than they really are. This change of color cannot be seen by the naked eye, but is detected with a special instrument called a spectrograph. Astronomers can use redshift to measure the speed at which an object travels. Redshift was actually used to help prove that the universe is ever-expanding.