The Sun's heat and light is needed to sustain life on Earth, but it won't always be around.
Scientists think the Sun has burned around half its supply of hydrogen. In about 5 billion years time, the hydrogen will run out. When that happens, other nuclear reactions involving carbon, nitrogen and oxygen will start. The Sun's core will contract and burn at higher temperatures, while the Sun as a whole will expand and eventually engulf the Earth. Its nuclear reactions will come to an end, leading to the collapse of the Sun. It will then become what is known as a white dwarf. Without a source of power, it will slowly fade into oblivion, finally becoming a black dwarf.
