Star colour and surface temperature (spec 8.7, 8.8)
Blue = hot; red = cool.
Stars come in a wide range of colours, and the colour reflects the SURFACE TEMPERATURE. This is the same physics as a piece of metal in a furnace β warm metal glows red, hotter metal glows yellow/white, very hot metal glows blue-white.
| Colour | Approx surface temperature (K) | Example |
|---|---|---|
| Blue | 10 000-30 000 | Rigel, Spica |
| White | ~7 500-10 000 | Sirius, Vega |
| Yellow | ~5 000-6 000 | Sun |
| Orange | ~3 500-5 000 | Aldebaran |
| Red | ~2 500-3 500 | Betelgeuse, Proxima Centauri |
Edexcel learning point. A blue star is HOTTER than a red star, even though "red hot" is the everyday phrase for something dangerously hot. In astronomy, the order is consistent: blue/UV emission requires the highest temperatures.
Spectral classes. Astronomers use the letter sequence O B A F G K M (from hottest to coolest) β not required to memorise for 4PH1, but worth knowing the Sun is a class G2 (yellow) star.
- Colour β surface temperature.
- Hottestβcoolest: blue, white, yellow, orange, red.
- Sun = yellow, ~5800 K.