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Star colour and temperature
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The colour of a star tells you how hot its surface is. Stars change colour as they evolve.
Classifying stars by colour
Stars can be classified by their colour.
A star's colour is related to its surface temperature.
From coolest to hottest: red, orange, yellow, white, blue.
The Sun is a yellow star. Blue stars are the hottest.
A star's colour is related to its surface temperature.
From coolest to hottest: red, orange, yellow, white, blue.
The Sun is a yellow star. Blue stars are the hottest.
Like a heated metal
A piece of metal heated in a flame glows red, then orange, then yellow-white as it gets hotter.
Hotter objects give out more of their light at shorter wavelengths, towards the blue end.
Hotter objects give out more of their light at shorter wavelengths, towards the blue end.
Colour changes as stars evolve
Sun-like star: nebula → main sequence (yellow) → red giant (cooler surface, so red) → white dwarf (hot, white, but small and dim).
More massive star: main sequence → red supergiant → supernova → neutron star or black hole.
More massive star: main sequence → red supergiant → supernova → neutron star or black hole.
Star A is red and star B is blue. Which has the hotter surface?
- Colour is linked to surface temperature.
- Blue stars are hotter than red stars.
Answer: Star B (blue)
Stars are classified by colour, which depends on surface temperature: red (coolest), orange, yellow, white, blue (hottest). A Sun-like star becomes a red giant and then a white dwarf; a massive star becomes a red supergiant, supernova, then neutron star or black hole.
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