What is the core of the Hertzsprung-Russell Diagram used for?

The Hertzsprung-Russell Diagram is a pivotal tool in astrophysics that primarily focuses on the relationship between a star's temperature and its luminosity. The diagram plots stars based on their absolute magnitude (luminosity) against their surface temperature (which is inversely related to color).

This relationship allows astronomers to categorize stars into different groups, such as main sequence stars, giants, and white dwarfs. By observing where a particular star lies on the diagram, scientists can infer critical information about its stage in the lifecycle and its physical properties. Thus, option C accurately captures the essence of the Hertzsprung-Russell Diagram's purpose in understanding not just current stellar characteristics but also broader implications for stellar evolution.

While the other options mention classifications or comparisons, they do not encapsulate the primary function of the diagram, which is to create a link between temperature and luminosity, key factors in the analysis of stellar types and their behaviors in the universe.