Georgina Guthrie, of Musselburgh School, asks :-

Ross Milburn, of King's High School, asked:-

What colour are stars?

Saskia Besier, a New Zealand graduate who is working towards a PhD degree in Astrophysics at the University of New South Wales, responded.

Stars are basically gigantic balls of fire and the best way to describe what colours they are is to think of the colours of fire. Stars aren't all the same temperature - some are hot and some are cool - and as their temperature changes so does their colour. Cool stars are red and orange like a match flame or a warm fire. Hotter stars are yellow like a roaring fire. Then as stars get really hot they become white, like sparks from a sparkler, and then blue like the flame of an arc-welding torch. Unfortunately from the ground and without a telescope most people cannot distinguish these colours but some people with very good eyesight can see if a star is white or blue or red, just by looking at them.

However these colours are not the only ones that stars have. There are many stars that are not as bright or not visible at all in the colour spectrum which our eyes detect but may have ""colours" which are outside of the visible spectrum. Some stars are bright in infra-red, ultra-violet, microwave, radio- wave, gamma-ray or x-ray light. We can only see this sort of light with the help of special telescopes and detectors.

The colours of stars is a very important part of Astronomy, particular- ly in the area called photometry. By looking at a stars' "colours" we can make important guesses on how hot it is, how old it is, how big it is and things like that.