What is the Hertzsprung-Russell diagram used for?

The Hertzsprung-Russell diagram is an important tool in the field of astronomy that categorizes stars based on their intrinsic brightness (luminosity) and their surface temperature (which is often represented by color). This diagram allows astronomers to visualize the relationship between these two fundamental properties of stars and effectively classifies them into different categories, such as main-sequence stars, giants, and supergiants, as well as white dwarfs.

When plotted on the diagram, stars will fall into specific regions that correspond to their evolutionary stages. For instance, the majority of stars, including our Sun, are found along the main sequence, where they spend most of their lifetimes fusing hydrogen into helium. The locations of stars on the Hertzsprung-Russell diagram provide insights into their age, composition, and future evolution, making it a vital tool for understanding stellar evolution and the lifecycle of stars.