H-R Diagram

• Hertzspring-Russell diagram
  • Named after Ejnar Hertzsprung and Henry Norris Russell
• Plots luminosity on the $y$-axis
  • Luminosity increases toward the top
• Plots either temperature or spectral type on the $x$-axis
  • Temperature increases towards the left
• Main sequence stars represent a relationship between temperature and luminosity that most stars follow
  • A band running from upper left (hot, more luminous) to the lower right (cool, less luminous)
  • Hotter stars are more luminous than cooler ones
  • More massive stars are hotter than less massive ones
    • More mass --> more gravity --> greater compression at their core
    • Greater compression at the core leads to better energy generation and thus more luminosity and heat
• Can be used to measure the distance of stars
  • See Measuring Distance from Earth here: star
  • Anchored by measurements of parallax

Astronomy Star