A star’s luminosity is fundamentally linked to its temperature and size.

The luminosity of a star is defined as the total amount of energy it emits per unit time, typically measured in watts. The temperature of a star is closely associated with the energy it radiates; hotter stars emit significantly more energy than their cooler counterparts. According to the Stefan-Boltzmann law, the energy emitted by a star is proportional to the fourth power of its absolute temperature, expressed mathematically as:

where $L$ represents luminosity and $T$ denotes temperature.

The size of a star also influences its luminosity. Larger stars possess greater surface areas from which to radiate energy, resulting in higher luminosity when compared to smaller stars that have the same temperature. However, exceptions exist; some smaller stars can outshine larger stars if they possess higher temperatures.

The relationship among a star’s luminosity, temperature, and size is effectively illustrated by the Hertzsprung-Russell diagram. This diagram plots luminosity against temperature and reveals distinct patterns that correlate with a star’s size and evolutionary stage. By analyzing a star’s position on the Hertzsprung-Russell diagram, astronomers can infer valuable information about its characteristics and evolutionary history.