Emerald Johnstone, of Queenstown, asks :-

Why is the Sun made of fire? Fire is feed by oxygen and there is no oxygen in space.

Murray Matthews, a nuclear chemist at the Department of Health's National Radiation Laboratory, Christchurch, responded.

We think of the Sun as a "fire" because it is so hot, and it even looks like a mass of flames when viewed through a telescope, but in fact it is not the normal type of fire we see here on Earth. The type of fire we are familiar with does need oxygen but the Sun does not get its energy from normal combustion. Instead, it gets its energy from nuclear reactions taking place in a region of extremely high gas pressure near its centre.

The Sun is a huge ball of gas, mainly hydrogen. Because of its enormous size, the gas within it is compressed due to the pressure of gravity. The extreme pressure near the Sun's centre heats the gas to a temperature of 14 million degrees Celsius, which is sufficient to start nuclear reactions like those which take place in a "hydrogen bomb". The Sun can thus be imagined as a continuously exploding nuclear bomb.

The main nuclear reaction taking place in the Sun is the combining ("fusion") of hydrogen atoms to form helium atoms. Some nuclear material is converted into energy in this process, and the released energy heats up the Sun even further. So much heat is released that the gases glow and emit visible light (daylight) as well as heat, and the great swirling masses of glowing gas seen through telescopes have the appearance of flames or "fire".