NOTES

Rotation of the galaxy causes the gaseous clouds present in the universe to become compact and due to the gravitation the process of nuclear fusion starts at the centre of this gaseous mass, converting hydrogen into helium. This process liberates an enormous amount of energy in the form of heat and light. At this stage the gaseous mass becomes a star. When star expands to a large size the temperature of the star at this stage also falls down, so it appears red. This is the Red Giant Star.