The sun is classified as a G-type main-sequence star, often abbreviated as G dwarf. It is situated in the middle of the Hertzsprung-Russell diagram, which categorizes stars based on their luminosity and temperature. In terms of temperature, the sun's surface reaches approximately 5,500 degrees Celsius (9,932 degrees Fahrenheit), which is cooler than hotter stars (like O-type stars) but warmer than cooler ones (like M-type stars). The sun generates energy through nuclear fusion, converting hydrogen into helium in its core, and this process releases the massive amount of light and heat that supports life on Earth.