The purpose of cosmology is to build a coherent theoretical framework allowing the comprehension of the universe (its future, its past) on a large scale. It owes its theoretical base with the general theory of relativity built by Albert Einstein in 1916. It was then applied to the study of the universe by Lemaître and Friedmann. Observational cosmology has, within this framework, for goal to confront this theory with the observations and to force its parameters. We will see in this chapter which are the bases, then we will describe the tools allowing to force it. Lastly, we will have the most recent results which made it possible to raise a little the veil on the contents of our universe.
The bases of cosmology are the general theory of relativity stated by Einstein in 1916, the metric one of Robertson and Walker who describes the geometry of the universe and finally, a tensor energy-impulse which describes the energy content of the universe. They melt the cosmological standard model baptized Big-Bang.