Image obtained from http://z.about.com/d/space/1/0/Y/Q/sun_tour.jpg
The Sun is a star at the center of the universe. Planets and other matter of the universe orbit the Sun which by itself alone is about 99.8% of the solar systems mass. The energy of the Sun, also known as sunlight, supports almost all of life on earth and drives the weather and climate.
It is comprised of 74% hydrogen, 25% helium, and 1% of trace quantities of other elements. This measurement is according to mass. The surface temperature of the Sun is approximately around 5,500 K degrees.
The Sun is a main sequence star, meaning it generates its energy by nuclear fusion of hydrogen nuclei into helium. The Sun is currently in state of hydrostatic balance, meaning that it is neither contracting nor expanding over time.
Image obtained from wikipedia