One of the approximately billion known stars in our Galaxy, the vast majority of the Sun's mass consists of hot gases. The sun emits radiation in the form of heat and light. Compared to the Earth, the diameter of the Sun is 109 times, the volume is 1.3 million times, and the mass is 333,000 times more. The sun moves around its axis at a speed of 70,000 km per hour and completes one revolution in about 25 days. The surface temperature of the Sun is 5500 °C, and the core temperature is 15.6 million °C. The sun's rays reach the Earth in 8.44 minutes. The Sun is the closest star to the Earth.