A star is nothing more than a ball of gases. Many stars, like Earth's sun, are made of helium and hydrogen. The sun and other stars convert hydrogen to helium in a process known as nuclear fusion. When a star converts all of its hydrogen into helium, it begins to die. Stars with plenty of hydrogen appear very bright in the sky and the more hydrogen a star uses, the more dim it appears.
Stars form in a gas and dust cloud. Gravity plays a major role in star formation, causing the gas to form near the center of the star. As the pressure from the gases increase, the star grows larger and hotter.Learn more about Astronomy