Although the sun is over one million kilometres away from us， we still feel its heat. In this sense， we can say that the sun is a very big fire ball.

　　The temperature on the surface of the sun is 6，000'C. The temperature is much higher deep inside the sun. If we could take a small piece of stuff¹ from the centre of the sun， dozens of cities would be burned down. This gives you an idea of how hot the sun is.