He studied at Caltech, and as a graduate student he specialized in the study of distant galaxies. One major characteristic of these galaxies is that they all have an observable redshift in their spectrum. Astronomers can only understand the universe by analysing the light the comes from a celestial object. A major way of breaking down the light for study is to split it into its component colors with a prism. When raindrops act as a prism, we get the rainbow.
Astronomers add a slit, which focuses the colors of starlight into a band.
Quantum mechanics describes how atoms absorb and emit light in only very specific colors. Whenever a gas of hot atoms glows, like on the surface of a star, we know in what colors that gas should glow. If a galaxy, which is composed of millions of stars, is coming toward us, or going away from us, those specific colors change just slightly. This is called the doppler shift , and is the same effect that causes a car's horn to change pitch as it passes you. If a galaxy is coming toward us, the specific colors of atoms become slightly bluer.