A star is a body of hot gas and dust that shines by its own light produced by nuclear fusion reactions. The nearest star to Earth is the Sun. When compared to other stars in the universe, the Sun is of average size, with a diameter of approximately 860,000 mi (1,380,000 km). Over a million Earth's could fit inside the volume of the Sun. The Sun is made up of gas (it is about 70% hydrogen and 28% helium), and is about 1.5 times as dense as water. The mass of the Sun is over 300,000 times that of Earth. Deep inside the Sun, nuclear reactions convert hydrogen to helium, changing matter to energy in a process called fusion. Fusion is responsible for converting over four million tons of the Sun's matter into energy every second.

The fusion reactions that take place within the Sun's, and any star's, core are the same as those...