What scientists use to classify stars?

Scientists classify stars based on several key characteristics, including their temperature, luminosity, size, and spectral type, which is determined by the absorption lines in their spectrum. The Hertzsprung-Russell diagram is a common tool used to visualize the relationship between a star's luminosity and temperature, allowing for further categorization into groups such as main sequence stars, giants, and white dwarfs. Additionally, the chemical composition of a star can also influence its classification.