The Hertzsprung-Russell Diagram is a graph that astronomers use to classify stars based on their brightness and temperature. On this diagram, stars are plotted with their temperature on the horizontal axis and their brightness on the vertical axis. This helps scientists understand the life cycle of stars and how they evolve over time.
Most stars, including our Sun, fall along a diagonal band called the main sequence. Stars on the left are hot and bright, while those on the right are cooler and dimmer. Other regions of the diagram include red giants and white dwarfs, which represent different stages in a star's life.