All stars begin as dust and tiny particles in a cloud of gas called nebulae. They develop into stars by passing through several stages over a period of millions of years. Once a star is born, it emits heat, light, x-rays, ultraviolet rays, gamma rays and other forms of radiation.
In a starﾒs early stages, it is cold and remains so until something, such as a comet, whizzes by, stirring up the particles by making them collide. Once the particles begin to collide, the clumps of dust and particles get bigger and bigger until the clump of dust has a mass strong enough for a gravitational pull. Over millions of years as the core of the clump becomes denser, it also becomes hotter until it develops into what is known as a protostar. When the protostar is extremely hot, approximately 7 million Kelvin, the process of nuclear fusion starts. Once the gravitational pull of the star is less than the pressure from nuclear fusion, the protostar combusts, releases heat, emits light and becomes what is known as a star.
A starﾒs brightness indicates how far away it is from the Earth and how much energy it releases. Brighter stars are either closer to the Earth, produce more energy or both. The color of a star also is an indicator of a starﾒs temperature. Stars that appear blue or white are extremely hot, whereas stars that appear orange or red are much cooler. A star continues to emit heat and light until it burns up all its gas.