Hertzsprung-Russell Diagram Animation In this video, the stars in globular cluster Omega Centauri are rearranged according to their intrinsic brightness (vertical axis) and their temperature (horizontal axis). The temperature of a star dictates its apparent colour, with cooler stars being red and hotter ones being blue. The majority of stars at any given time fall into a wide band known as the main sequence, which passes from the top left (hot, bright stars) to the bottom right (cool, dim stars)