The star around which the planet Earth orbits. The Sun is a G-type main-sequence star, has a mass of 1.9 × 10³⁰ kg and a volume of 1.41 × 10¹⁸ km³. It is composed mostly of hydrogen, which fuses in its core during a thermonuclear fusion reaction called the p-chain into helium and other elements. The temperature at the centre of the Sun is approximately 15 million kelvin. Above the core is the radiative zone and even higher up is the convective zone. The visible surface is called the photosphere and has a temperature of 5,780 kelvin. It glows yellow-orange. The Sun consumes approximately 700 million tonnes of hydrogen per second and produces 3.8 × 10²⁴ kW of energy, only a small fraction of which reaches the Earth’s surface, where it makes life possible.