A star is a huge glowing ball of hot gas mainly hydrogen and helium the Temperature is so high in its core nuclear fusion occurs producing energy the outward pressure of gas heated by fusion is balanced by the inward pull of gravity leaving the star in hydrostatic equilibrium this balance of force last for most of the stars life maintaining its steady temperature radiation and convection carry the energy from the core out through a stars atmosphere when the energy gets high enough in the atmosphere that the region above it is transparent it escapes out into space as light of all wave lengths as well as stellar wind through stars may appear static they rotate and vary in luminosity there are hundreds of billions of stars in the Milky Way galaxy alone among them is our sun the closes star to earth