The sun will last approximately another five billion years, according to NASA in 2012. The sun's light and heat are generated by the burning, or fusing, of hydrogen gas into helium gas.
The temperature at the sun's core, where the hydrogen fusion reaction takes place, is 15 million degrees Kelvin or about 27 million degrees Fahrenheit. Since its birth 4.6 billion years ago, the sun has used up approximately half its hydrogen fuel. As the sun's supply of hydrogen gas is gradually burned up, it will become cooler and larger, a so-called Red Giant. It is thought that at that point, it will swallow up Mercury, Venus and Earth, which are the three planets closest to it in orbit. After the hydrogen is used up, the sun will continue to burn whatever fuel remains until all have been exhausted.