HR (Hertzsprung-Russell) diagram

The Hertzsprung-Russell (H-R) diagram is a graphical tool used by astronomers to categorize stars based on their brightness and temperature. The vertical axis represents a star's brightness, while the horizontal axis represents its temperature, which decreases from left to right. Most stars, including our Sun, fall along a diagonal band called the "main sequence." This diagram helps scientists understand stellar evolution, showing how stars of different types and ages develop over time, from birth in nebulae to their various end stages, such as becoming red giants or white dwarfs.