How old is the universe? What evidence is there for the Big Bang? What are stars and galaxies made of?
All these different questions can be answered by looking at rainbows.
A powerful tool for learning about the evolution of our universe is observing the the rainbows of light given off by stars and galaxies. The rainbow pattern formed by light of different sources is called a spectrum. Spectroscopy is the analysis of the light spectrum. Since stars and galaxies give off light, much can be learned about them through the study of spectroscopy.
Looking at the spectra of light that stars and galaxies give off, scientists have observed some interesting things.
Spectroscopy tells us what stars and galaxies are made of.
Since different kinds of materials have slightly different spectra, scientists can use a star's spectrum to figure out what it is made of.
Spectroscopy tells us about the position and movement of stars and galaxies.
Spectroscopy can also be used to tell us about the distance and movement of stars and galaxies. By observing the spectra of galaxies, scientists have discovered that some are moving away from us. Spectra from some galaxies appear to be redshifted. Red is a slower the frequency of light which has a longer wavelength. Objects moving away appear to have longer wavelenths, and hence have a redshift. The greater the redshift, the faster a galaxy is moving away from us. Furthermore, the faster a galaxy is moving away from us, the further away that galaxy is.
By observing redshifts, scientists are able to show that the universe is expanding, which is important evidence for the Great Radiance (a.k.a. Big Bang.) This redshift is the basis of Hubble's Law, which states that the degree of redshift in light is proportional to its distance from us. That is, the more red-shifted a galaxy is, the farther away it is.
Spectral lines of the sun (left) shift toward red in a supercluster of distant galaxies (right). The further away a galaxy is, the faster it moves away from us. This is detected as a redshift. Hence, in stars moving away from us, the spectral lines appear to shift in the direction of red.