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
Examiner Tip
We often remember red as being hot and blue as cool in everyday life, but remember this is the other way around when describing the temperature of stars!
