ABSTRACT
The main building blocks were stars that formed into massive aggregates called galaxies and these varied considerably in size and nature. Most were spiral in shape and contained, typically, about 100000 million stars. Others were elliptical in nature and others irregular. Astronomers realize that the nature and physics of the Universe in the instant immediately after its creation is beyond present knowledge and understanding if the theoretical extrapolation back in time is accepted. The cosmological principle and the expansion of the Universe formed the only basis for considering its evolution as a whole in the immediate post-war years. The radiation had to be cosmic in origin, and measurements at other wavelengths showed it was consistent with Planck radiation at a temperature of about 3° Kelvin. In the early stages of the Universe, the matter would be very hot and very dense, and would be opaque to radiation.
