The Sun is the star at the center of our Solar System and is an enormous sphere of hot plasma primarily composed of hydrogen (~73%) and helium (~25%). It formed about 4.6 billion years ago from the gravitational collapse of a molecular cloud and is classified as a G-type main-sequence star or yellow dwarf. With a diameter of roughly 1.39 million kilometers—about 109 times that of Earth—it holds 99.86% of the Solar System's mass. The Sun's core temperature reaches around 15 million degrees Celsius, where nuclear fusion converts hydrogen into helium, releasing enormous energy that powers the Sun and sustains life on Earth. The Sun's visible surface, or photosphere, is about 5,500 degrees Celsius (nearly 10,000 degrees Fahrenheit), while its atmosphere includes layers such as the chromosphere and the corona, which extends millions of kilometers into space. Sunspots—cooler, darker areas—appear on the surface as part of an approximately 11-year solar cycle that affects solar activity and magnetic phenomena like solar flares and auroras. The Sun's magnetic field is very strong and shapes the solar wind, a stream of charged particles that creates a magnetic bubble called the heliosphere around the Solar System. Without the Sun's energy, Earth would be a frozen wasteland, making it essential for climate, photosynthesis, and life itself. Looking ahead, the Sun has enough nuclear fuel to burn steadily for another 5 billion years before swelling into a red giant and eventually shrinking into a white dwarf fading over time.