ABSTRACT
This chapter describes how the Big Bang started a Universe that would later form clusters, galaxies and apparently countless quantities stars. The evolution of these stars, process the light elements hydrogen and helium into the elements we observe, including the elements needed for the development of life. A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun. Other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. The contraction of the core releases large amounts of gravitational potential energy that cause an increase in hydrogen burning in a shell surrounding the core. For star like our sun, this eventually leads to the expansion of the star's outer layers which is accompanied by a drastic increase in the star's luminosity.
