The Sun is the central star of the Solar System. It is a nearly perfect ball of hot plasma that has been heated to incandescence by nuclear fusion processes in its center and radiates energy mostly as visible light, ultraviolet light, and infrared radiation. It is by far the most essential source of energy for Earth’s life. It has a diameter of approximately 1.39 million kilometers (864,000 miles), or 109 times that of the Earth. It has a mass around 330,000 times that of Earth and contributes for approximately 99.86 percent of the total mass of the Solar System. Roughly three quarters of the Sun’s mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon and iron.