ABSTRACT
This chapter reviews the observational basis for the standard cosmology. The evolution of the Universe is based upon the Friedmann-Robertson-Walker cosmological model, or the hot big bang model as it is usually called. The model is so successful that it has become known as the standard cosmology. The age of the Universe can be measured in a variety of different ways. There are: by using the expansion rate of the Universe to compute the time back to the bang; by dating the oldest stars in globular clusters; by dating the radioactive elements; by considering the cooling of white dwarf stars; by calculating the cooling time for hot gas in clusters and so on. The cosmic microwave background radiation (CMBR) provides the fundamental evidence that the Universe began from a hot big bang. The remarkable uniformity of the CMBR indicates that at epoch of last scattering for the CMBR the Universe was to a high degree of precision isotropic and homogeneous.
