Of the many bodies in our solar system, the Sun is the largest. It contains 99.86% of the total mass in our solar system and could fit roughly 1.3 million Earths. The Sun is hot enough to undergo thermonuclear fusion, when hydrogen fuses together to form the heavier element, helium. It is an oblate spheroid, or the closest thing to a perfect sphere observed in nature. The science of studying the sun is called heliophysics. It is about 93 million miles from Earth and plays a vital role in the survival of all the organisms living on the blue planet