What is Star?
[[File:Antares - Eso1726a.tif|right|260px|thumb| Reconstructed view of the surface of the star [[Antares]] in the constellation of [[Scorpius]]]] [[File:Starsinthesky.jpg|right|260px|thumb|A star-forming region in the [[Large Magellanic Cloud]]. [[NASA]]/[[ESA]] image]] [[File:Pismis 24.jpg|thumb|right|260px|The open star cluster [[Pismis 24]] is in the [[nebula]] [[NGC 6357]]. It has some of the largest stars known. Pismis 24-1 has nearly 300 times the [[mass]] of the [[Sun]]. It is a multiple system of at least three stars. <br/> The strange shapes taken by the clouds are a result of the vast [[radiation]] emitted by these huge, hot stars. <br/>This image combines image data with three different [[filter]]s in visible light from the 1.5-metre [[Denmark|Danish]] telescope at the ESO La Silla Observatory in [[Chile]].]] [[Image:Crab Nebula.jpg|thumb|250px|right|The [[Crab Nebula]], remains of a [[supernova]] that was first seen around 1050 AD]] A '''star''' is a very large ball of bright, [[wikt:glow|glowing]], hot [[matter]] in space. That matter is called [[plasma (physics)|plasma]]. Stars are held together by [[gravity]]. They emit [[light]] because they are very hot. The [[Sun]] is an example of a star. It is at the center of the [[solar system]]. The amount of material in a star (its [[mass]]) is so huge that a [[nuclear reaction]] called [[nuclear fusion]] goes on inside it. This reaction changes [[hydrogen]] to [[helium]] and gives off heat. The light and heat created by nuclear fusion makes stars very hot. It also makes bigger [[chemical element]]s. In the Sun (but not all stars) the change which takes place is the production of [[helium]], with small amounts of heavier [[Periodic table|elements]]. Stars have a lot of [[hydrogen]]. Fusion makes a lot of energy. The energy produced by stars moves ([[radiation|radiates]]) away from them. Much of the energy leaves as light, and the rest leaves as other kinds of [[electromagnetic radiation]]. When a star like the Sun gets old, it will expand in size and