The Hertzsprung-Russell diagram is one of the most important representations in astronomy: if the luminosity of stars and their temperature are plotted together, they are arranged in characteristic areas of the diagram. Most of them lie on the so-called main sequence, for which hot stars are particularly bright and cooler stars rather faint, and in the middle of which lies the Sun. But there are also, for example, particularly bright cool stars, the red giants, and hot but faint white dwarfs. Together we will take a look at the history of the development of this diagram, which at first glance seems strange, and learn how to read it.
