The star that shares the solar system with the Earth is the Sun. It is the star around which all the planets in the system revolve. According to About.com, the Sun weighs almost 99.86 percent of the total mass in the solar system.
The Sun is 93 million miles from the Earth and, at times, as close as 29 million miles from Mercury, the closest planet to it. The Sun is composed of several layers: the core, the radiative zone, the convection zone, the photosphere and the corona. The photosphere is the part people on Earth see. The Sun is absolutely necessary to sustain life on the Earth.