The sun is classified as a G-type main-sequence star, often referred to as a G dwarf star. It lies within the Hertzsprung-Russell diagram, which categorizes stars based on their luminosity and temperature. The sun has an average surface temperature of about 5,500 degrees Celsius and is fueled by nuclear fusion, converting hydrogen into helium in its core. This process generates enormous amounts of energy, providing light and heat essential for life on Earth.