The Sun
| Diameter | 1,392,530 km |
| Average distance from Earth | 149,597,900 km |
| Temperature | 6,000 degrees Celsius at the surface 14 million degrees Celsius at the centre |
| Period of rotation | 25 days at the equator 35 days at the poles |
First photograph taken of the sun
through Sydney Observatory's new
solar telescope. Photo: Geoff Wyatt
The largest and most prominent feature of our solar system is the star at its centre called the Sun. It is a big ball of very hot gas held together by gravity, providing the light and most of the heat for the solar system. One hundred and nine Earths or 463 Australias could fit side to side across the Sun's equator, a distance of more than one million kilometres. Inside the Sun 1,300,000 Earths would be needed to fill it up.
The Sun's energy is produced deep within its centre. At the centre the temperature (15,000,000 degrees Celsius) and pressure (200,000 million times the air pressure at the Earth surface) are so high that nuclear fusion reactions can take place, turning hydrogen into helium. The energy produced takes about one million years to reach the Sun's surface where the temperature drops to 6,000 degrees Celsius.
The visible surface looks yellow and has a mottled, grainy appearance due to the chaotic eruptions of energy at the surface. Dark spots called sunspots can also be seen on the surface. Bright eruption of hot gas from the surface are called solar flares.
The Sun has been shining for about 4,500 million years and has enough fuel to keep shining for another 5,000 million years or so. At the end of its life it will expand until it becomes so large all the planets out to Venus will be gobbled up by the Sun. It will shine for another 1,000 million years as a red giant until it suddenly shrinks to become a white dwarf star. Our Sun will then spend the rest of its life as a tiny white dwarf star about the size of the Earth. Over trillions of year the little star will grow slowly colder.
