SUN

Spacecraft have not only given us spectacular views of the planets, they have also been used to study the stars and galaxies.

Our own star is the Sun and we have been able to obtain spectacular views of it both from the US manned space station Skylab, and from later unmanned craft.

The Sun may look small in our sky, but it is a really huge globe of gas 1.4 million kilometers across. Most of the Sun is hydrogen, and the temperature and pressure are so great at its centre that nuclear fusion takes place. This is what powers the Sun a might nuclear core.

In the Sun, hydrogen atoms are welded together to form helium. While this is happening, a tiny amount of mass is converted to energy, which streams out, causing the Sun to shine.

Because it is gaseous, and spins once in twenty seven days, the Sun often suffers massive explosions on its surface but we are too far away to suffer serious damage from its disturbances. Spacecraft and astronauts are not so lucky. They have to take special precautions to avoid the harmful effects of solar radiation, which can destroy sensitive electronic devices and even more sensitive living tissues.