The Hertzsprung-Russell (HR) diagram is a graph of the luminosity of stars (vertical axis) against their surface temperature (horizontal axis). It is used to classify stars and to show how they evolve.The axes have two unusual features:
• temperature increases to the left, from about 3000 K on the right to about 40 000 K on the left;
• both axes use logarithmic scales, because the luminosities of stars range from about 10−4 to 106 times the Sun's luminosity (L☉).
• Red giants: above the main sequence on the right. They are cool but luminous because they are very large.
• Red supergiants: at the top right. They are even larger and more luminous.
• White dwarfs: at the bottom left. They are hot but have a low luminosity because they are very small.The evolution of a star can be drawn as a path on the diagram. The Sun will move from the main sequence up and to the right to become a red giant, and then down and to the left to become a white dwarf.
• temperature increases to the left, from about 3000 K on the right to about 40 000 K on the left;
• both axes use logarithmic scales, because the luminosities of stars range from about 10−4 to 106 times the Sun's luminosity (L☉).
• Red giants: above the main sequence on the right. They are cool but luminous because they are very large.
• Red supergiants: at the top right. They are even larger and more luminous.
• White dwarfs: at the bottom left. They are hot but have a low luminosity because they are very small.The evolution of a star can be drawn as a path on the diagram. The Sun will move from the main sequence up and to the right to become a red giant, and then down and to the left to become a white dwarf.