Explain how the age of a globular cluster can be determined from its zero-age main sequence plot for a H-R diagram

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Explain how the age of a globular cluster can be determined from its zero-age main sequence plot for a H-R diagram

  • Star cluster – ’00 000s of stars of similar age (form from same cloud at same time).
  • 2 types: globular (older and more stars and open)
  • Determine age by turn off point i.e. where it leaves main sequence
  • Older – lower turn off
  • Younger – higher
  • Past turn off – larger/more massive stars become red giants
  • Older have lower turn off because most stars are already past main
  • Turn off determined when majority of stars are no longer main sequence