Star
a giant ball of hot gas that creates and emits its own radiation through nuclear fusion. Stars are arranged in various classes by their spectral characteristics. The chief classes are identified by the letters O, B, A, F, G, K, M. Each class contains ten subdivisions numbered from 0 to 9. The classes define a temperature or color sequence. Stars of type O and B are Blue-white and have high temperatures (35,000°K / 20,000°K); A stars are white, temperature 10,000°K; F and G stars are yellowish, temperature 7,000°K; K stars are orange, and M stars are red, temperature 3,000°K. Wolf-Rayet stars are hot, blue giants. They are extremely turbulent and have a temperature of 50,000 °K and higher