A medium-sized,main-sequence star located in a spiral arm of the Milky Way galaxy,orbited by all of the planets and other bodies in our solar system and supplying the heat and light that sustain life on Earth. Its diameter is approximately 1.4 million km (868,000 mi),and its mass,about 330,000 times that of Earth,comprises more than 99 percent of the matter in the solar system. It has a temperature of some 16 million degrees C (27 million degrees F) at its core,where nuclear fusion produces tremendous amounts of energy,mainly through the series of reactions known as the proton-proton chain. The energy generated in the core radiates through a radiation zone to an opaque convection zone,where it rises to the surface through convection currents of |