The Sun is the nearest star to the Earth and is the centre of our Solar System. Like all stars, it is a ball of hot gas within which nuclear fusion takes place. The Sun, which was born some 5,000 million years ago, has a temperature at its centre of around 14,000,000OC, whereas the surface is a cooler 6,000 OC. It is no longer the only star known to have a system of planets around it (astronomers are discovering others all the time) and is the provider of energy for life here on Earth. Indeed, all energy sources can be traced back to the Sun and, without it, life here on Earth would quite simply not exist. The Sun is not only extremely hot, it is immense in size. It has a mass of approximately 1.99×1030kg and a diameter of 1,392,000km and is 149,000,000km away from the Earth. Even so the the Solar System is rotating about an axis. However, unlike the planets, and because its surface consists of layers of gas, different parts of the Sun rotate at different speeds. The middle part, around its equator, takes around 25 days to rotate once, whereas the top and bottom, around the poles take about 30 days.