What two stellar properties are primarily related and plotted on the Hertzsprung-Russell (H-R) diagram?

💡 Explanation:

The Hertzsprung-Russell (H-R) diagram is a pivotal tool in astronomy that visually represents the relationship between a star's intrinsic brightness, or luminosity (vertical axis), and its surface temperature, or spectral type/color index (horizontal axis). It is fundamental for understanding stellar evolution.