Why do stars shine?

Stars shine because of nuclear fusion in their cores. In this process, hydrogen atoms fuse to form helium, releasing immense amounts of energy in the form of light and heat. This energy travels outward through the layers of the star and radiates into space. The balance between gravitational pressure and the outward force of fusion keeps stars stable. The colour and brightness of a star depend on its size, temperature, and distance from Earth, with hotter stars appearing blue and cooler stars appearing red.