The Sun isn't really a planet but a Star. In astrology it's refered to as one of the lights, the Moon being the other. It too revolves around a center called the barycenter. In a personal Natal Birth Chart the Sun rules leadership, character, your soul, your ego be it strong, weak, or well developed. The Sun rules your drive. leadership abilities, ego and your life force.
The Sun times our year. The Cardinal Ingress, the times that the Sun enters the 4 Cardinal signs and starts our 4 seasons, marking definitive points in our year! There are 12 Sun signs.
To find out how the Sun's transits affects you