Audio Guide：

Danish and American astronomers Ejnar Hertzsprung and Henry Norris Russel found that the brightness of a star is closely linked to its surface temperature. They drew up the famous Hertzsprung-Russell diagram to indicate the relationship between the luminosities and surface temperatures of stars. In the H-R diagram, most stars fall into the main sequence regions on the diagram, the diagonal going from the upper left to the lower right. Stars on this band are called main-sequence stars. Stars remain in this phase for the most part of their lives. Stars on the upper right are red giants and red supergiants with low surface temperature, large volume, and intense brightness. On the lower left of the diagram are the white dwarfs. They are high in temperature but small in volume and low in luminosity. White dwarfs represent the final stage in a low-mass star’s process of evolution.