What Determines the Position of a Star on the Main Sequence?

A star's position on the main sequence is primarily determined by its mass. High-mass stars are more luminous and hotter, and they appear on the upper left of the Hertzsprung-Russell diagram. Conversely, low-mass stars are less luminous and cooler, appearing on the lower right. The mass of a star influences its core temperature and pressure, which in turn affects the rate of hydrogen fusion.