Hertzsprung-Russell Diagrams (Edexcel IGCSE Physics)

• Stars are classified using the Hertzsprung-Russell (HR) diagram
• This is a plot of:
  • The luminosity on the y-axis
    • This is from dim (at the bottom) to bright (at the top)

  • The temperature on the x-axis
    • This is from hot (on the left) to cool (to the right)
    • This is normally in Kelvin

The Hertzsprung-Russell Diagram

• The main features of the Hertzsprung-Russell diagram are:
  • Most stars lie on the Main Sequence. This is the band of stars going from top left to bottom right
  • Below the main sequence (and slightly to the left) are the White Dwarfs
  • Above the main sequence on the right-hand side are the Red Giants
  • Above those are the Red Supergiants

• This means the white dwarfs are dimmer and hotter than the red giants which are brighter and cooler
• Sometimes, the absolute magnitude is on the y-axis instead
  • Remember this will still go from dimmest (highest number) at the bottom to brightest (lowest number) at the top!