The Sun is the star at the center of our solar system. It has an immense diameter of about 1.4 million kilometers and a mass of about 2 x 10^30 kilograms, accounting for over 99% of the total mass of the solar system. The Sun is made up of about 73% hydrogen, 25% helium, and 2% other elements. Its core temperature is around 15 million degrees Celsius, where nuclear fusion occurs and produces the energy that provides light and heat for our planet. The Sun has an 11-year cycle of activity, marked by changes in the number of sunspots and solar flares. It also has a powerful magnetic field that can affect Earth and produce auroras.