The sun is classified as a G-type main-sequence star, or G dwarf star, in the Hertzsprung-Russell diagram. It is primarily composed of hydrogen (about 74%) and helium (about 24%), with trace amounts of heavier elements. The sun generates energy through nuclear fusion, a process where hydrogen nuclei combine to form helium at its core, releasing vast amounts of energy in the form of light and heat. This energy is crucial for life on Earth, providing warmth and driving weather patterns, photosynthesis in plants, and the overall sustenance of various ecosystems.