Sun

**Dark patches on the sun's surface are called sun spots.These spots are about 1500°C cooler than the rest of the surface.They are caused by flowing gas inside the su creating magnetism that restricts light and heat from certain parts of the surface.the overall number of sun sports varies,rising to a maximum and decreasing again over am 11-years cycle.**
 * [[image:http://solar.physics.montana.edu/canfield/ssu_images/thumb_sunspots.gif width="233" height="203"]] sun spots ** [[image:http://t3.gstatic.com/images?q=tbn:daa3rbdqhrHy0M:http://theradiokitchen.net/wp-content/uploads/image/sunspots.jpg width="234" height="202"]]


 * The sun is a star with the scientific name SOL.It is just one of many,but of course very important to us. **

= What is the Sun made of? = ** The Sun is a mixture of gases - approximately 75% hydrogen and 25% helium. These proportions are changing over time as reactions in the Sun's core convert hydrogen into helium. It's the energy released by these reactions which produces the Sun's heat. At the Sun's core, where the temperature is 15 million kelvin, the gases are compressed by gravity to a density many times that of lead. While this gravity tries to shrink the core, the Sun is kept in equilibrium by the counterbalancing force of the energy released as the hydrogen burns. **


 * Away from the core, both the density and temperature of gases decrease quite quickly. Heat radiates outwards through a 'radiative zone' until it reaches the photosphere. **


 * The photosphere - which you could think of as the surface of the Sun - even though it's not solid - lies beyond the radiative zone. It is a layer about 500 kilometres (300 miles) thick, where the temperature is a 'cool' 5 800 kelvin. **