Besides white stars， there are also yellow， red and blue ones. The colour of the star is decided² by its temperature. When we put a piece of iron over a fire， it becomes red first； when it becomes hotter， the colour yellow； finally， when it is very， very hot it becomes blue. Like the iron， the blue stars have the highest temperature. The temperatures of the blue and white tars¹ reach thousands of degrees while yellow and red stars are not so hot. They are about several thousand degrees.

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