Classification of Stars (Edexcel IGCSE Physics (Modular))

Classification of stars

• Stars come in a wide range of sizes and colours, from yellow stars to red dwarfs, from blue giants to red supergiants

  • These can be classified according to their colour

• Warm objects emit infrared and extremely hot objects emit visible light as well

  • Therefore, the colour they emit depends on how hot they are

• A star's colour is related to its surface temperature

  • A red star is the coolest (at around 3000 K)

  • A blue star is the hottest (at around 30 000 K)

Star colour and surface temperature

The colour of a star correlates to its temperature. The bluer the star, the hotter its surface temperature. The redder the star, the cooler its surface temperature

• Astronomical objects cool as they expand and heat up as they contract

  • This means that their colour will also change according to their surface temperature

• When a star becomes a red giant it becomes redder as it expands and cools

• When a star becomes a white dwarf it becomes whiter as it contracts and heats up