Colours of Stars

Constellation of Orion
Credit: Rogelio Bernal Andreo

Stars come in lots of different colours, and their colour depends on the temperature of the star.

We find that small stars are cool (less than 3000°C) with a red-ish appearance, whereas big heavy stars are hot (over 30,000°C), and have a blue-ish glow. At about 6,000 °C, the Sun is considered to be on the cooler side and, as we all know, has a yellow-ish look about it.

In fact, the temperature of a star, and therefore its colour, actually depends on the amount of mass it has. Very massive stars, which can be over ten times the mass of the Sun, are the hottest, and smaller stars, with less than half the mass of the Sun, are the coolest.

Although they are bigger, the hot, blue stars do not "live" as long as the smaller ones, because they use up their nuclear fusion much more quickly. The hottest stars will only live for a few million years, whereas the smallest stars will live for hundreds of billions of years.

Our Sun is around halfway through its 10 billion year lifetime.